Allow for shifts >24h

[jeriox]

shifts longer than 24h?

          is it a good idea that we just shift the start time by one day but not the meeting time? (can also be a part of rethinking shifts with respect to >24h to get the bugfix out quickly)

Originally posted by @jeriox in https://github.com/ephios-dev/ephios/pull/1059#discussion_r1317578534