When it comes to closing your event, there are 2 separate fields you'll deal with.
The first field is the Event Date field (in Event Setup > Event Details), which controls when people can register to attend your event. By default, the event will stay open for registrations until midnight after the Event Date. You can manually close your event registration on or before the Event Date in Peer-to-Peer events by clicking the green dot in the Public Registration section on the Dashboard, or by clicking on the dropdown next to the name of your event in the top menu toolbar.
The second field is the Peer-to-Peer Pages Expire field (in Event Setup > Event Details), which controls how long your Participants' fundraising pages will stay open for donations. The default length is one month after the Event Date.
Note: The countdown timer displayed on the Event Web Page and the fundraising pages is based on the Event Date and the Start Time (both in Event Setup > Event Details). The countdown timer does not affect when your event will close or how long your Participants' fundraising pages will stay open. It simply shows how much time is left until the start of the event.
Things to know:
If you don't manually close registration, your event registration will automatically close at midnight after your Event Date.
Closing your event does not affect your participant's fundraising pages, which stay open for a default 1 month after your Event Date. Your event does not need to be open for your fundraising pages to stay open.
Since Crowdfunding Campaigns (such as #GivingTuesday, year-end, and other project-based campaigns) do not have fundraising pages, once the campaign closes, your donors are no longer able to give.
The countdown timer on the Event Web Page and fundraising pages simply shows the time remaining until the start of the event.