My guess is that Saturdays between Morning Mass and Vigil Mass is a good time because it would suit those who work Mon-Fri, it would suit retirees who no longer like going out at night, and theoretically would be easier for parents with children to take turns at attending.
Your circumstances will be different, so adjust accordingly.
We have a 9am Saturday morning Mass, and a 5pm Vigil Mass.
The 9am Saturday morning Mass is preceded by the Morning Prayer of the Church and followed by a short time of Exposition of the Blessed Sacrament that culminated in Benediction around 10am. During Exposition, the Confessional is open for business.
After Benediction the Rosary is prayed.
We also have a large meeting room equipped with Audio Visual stuff, in the same building as the Church.
For our circumstances, that means morning tea starting around 10.25am in time for the Monthly Plenary Council Steps to begin at 10.45am should work. Start with a prayer calling upon the Holy Spirit and a prayer invoking the aid of Mary, Help of Christians.
Part 1: Missionary and Evangelising (30mins)
Either get a past graduate of an RCIA program in the parish to come and tell his/her conversion story in 15-20 mins with the remainder of the 30 minutes filled with question time or general discussion time. However it is going to more likely be question time, since apart from the conversion story itself, you will want to ask questions about what helped or hindered that 'journey home' and what were the catalysts that started opening up his/her heart and mind, and what they think would have been helpful to them as a newbie at Mass.
Alternately find one of the first Monday Journey Home programs from the Coming Home Network. They have the first half hour as testimony and the last half hour for question time. Find one of them and together watch the first half.
Part 2: Inclusive, Participatory and Synodal (30 mins)
In every parish there are people with hearing aids, low vision, walking sticks, wheelchairs, others recovering from surgery, or who have special needs children, or who are battling depression and treatment for cancer. Ask one of them, or two of them with the same set of difficulties to come, and to talk about their regular routine in getting to and from Mass, any struggles they have during Mass, anything they think would make access and participation easier for them. Use any remaining time of the 30 minutes as question time or discussion time.
Over time this should lead us to a greater awareness of the needs of others, a deeper compassion for each other, and maybe some simple practical improvements.
Part 3: Prayerful, Sacramental and Eucharistic (10 mins)
Send everyone off into the parish church for 10 minutes of personal prayer.
(Since not everyone is going to make it to the time of Exposition before Benediction)
Lunch Time (30 mins)
Part 4: Humble, Healing and Merciful (30 mins)
This is alone time with God and the aid of a notebook and pen.
Think about the people in your life with whom you are not at peace, write down their names, and ask for God's help to forgive them, and then seek forgiveness from God for holding onto resentments. Then pray a prayer for each person on that list, asking God to bless them and bring them closer to Himself. If there is anything practical that God prompts you to do for one or more of them, write it down, and make it a priority to do it.
If any time remains, make a list of everyone you know who is sick, seriously ill or suffering, and then pray for each one of them individually.
Part 5: A Joy-filled, Hopeful and Servant Community (30 mins)
With the same notebook and pen write down three blessings of the past week or month that you want to give God thanks for, and then write a paragraph about a time in the past month where you knew God was active in your life (eg saved from an accident, a chance meeting with someone who had the exact answer you had been looking for, an unexpected supernatural peace after hearing disturbing news). That should take no more than 10-15 mins, then share it with 2 or 3 others in the group, and listen in turn to their blessings and stories.
It is only when we stop and look back that we can more clearly see where God has been active in our lives. Gratitude leads us to joy, and sharing our reasons for gratitude increases our trust in God – which leads to hope.
Afternoon tea break (20 mins)
Theme 6: Open to Conversion, Renewal and Reform (1 hour)
From the Gospel passages for the next 4 Sundays, select a single chapter, and have copies of that Gospel chapter printed out. Give everyone a copy, and then direct each one to find a place to be alone with God, to slowly read through that Gospel chapter and then ask God what dreams He has for you, what things He would like to see happen in your family life, work life, ministry life, community life, and write down any ideas and out-of-the-blue thoughts that come, and write them down in your notebook. You may need to start by writing down your own dreams, and then ask God if they align with His dreams, or if they are big enough to match the dreams He has for you. Towards the end, place all the dreams in His hands and ask Him to confirm for you which ones come from Him and which you should work on, and which ones are not from Him and which you should gently let go of.
Conclusion: Come back together and pray a simple prayer, (eg Our Father) as a conclusion, and then invite anyone who would like to take the option to stay and talk, or who would like someone to pray for them to remain.
In more condensed form that looks like:
Morning Tea 10.25am
Conversion Story + Q&A 10.45am
Disability & Inclusion Story + Q&A 11.15am
Personal Prayer 11.45am
Praying for Relationships in tension 12.25pm
Sharing our Blessings 12.55pm
Afternoon Tea 1.25pm
Dreaming with God 1.45pm
Conclusion 2.45pm (prayer requests and having a chat might take that to 3.30pm)
A monthly period of recollection is something the Church encourages with a partial indulgence, and a monthly day like this would qualify.
Of all these things, if you could only do a few of them, make Dreaming with God and Praying for Relationships in tension the priorities.
If you wanted something like this to form the backbone of your parish response to the Plenary Council, go for it. You wouldn't even need to wait for the first session of the Plenary Council to begin. It is something that could start quickly and with not much to do for set up (pray, find speakers, set up meeting room, arrange tea & coffee, provide pens & paper, print off Gospel chapter, work out whether BYO lunch or a tray of pre-prepared sandwiches would suffice)and not much by way of cost.
Small do-able steps inspired by the 6 Themes, like the ones above, can have a very big long term impact.