The invitation says the workshop begins at two. The room booking also begins at two. By the time someone has found the chairs and arranged the materials, participants are waiting in the doorway. The calendar looked tidy because it recorded the public activity but left out the work around it.
Draw three blocks on the timetable
Separate access and setup, the advertised activity, and clearing away. For an imagined workshop, the group might request the room from 1:30 to 4:30, with the public session from 2:00 to 4:00. Those half-hours are proposals to agree with the venue, not an entitlement created by writing them down.
Check when the keyholder is available and when the previous group must be out. Access to a building may differ from access to the particular room. Put the confirmed details next to the timetable so nobody has to reconstruct them from several messages.
Test the handover at both ends
Who receives the room, and what condition should it be in? Who checks it before leaving? Decide where furniture returns, how rubbish is handled and whether equipment can remain between activities. A shared room can serve very different groups in the same afternoon.
Our guide to sharing the jobs at the end of an event helps assign the work. The booking question comes earlier: is there actually time available for those jobs before the next group arrives?
Publish the participant time clearly
The volunteer timetable and public invitation have different audiences. Someone attending the workshop needs the welcome time and finishing time, not a confusing mixture of access windows and key collection arrangements.
Send helpers a separate, short schedule that identifies their own arrival time. If the venue cannot provide the requested setup period, adjust the activity or booking before announcing it. A smaller arrangement prepared calmly is often easier to deliver than an elaborate plan that depends on getting into a room early without agreement.