Sign in is also weigh-in and squad sign ups in my experience. This is an important consideration if you are trying to squad with a specific person or group, or want to start/finish at a particular stage/location. Generally you can put in multiple people when you squad, so that can reduce the need to be present during the squadding, but every match has the potential to be different.
Weighing and chronographing can take a while. I do try to show up to the range ready to go at the start time given, and even then I have have had less than 100% success in getting the squad I "want". I mostly shoot teams, so there is an added difficulty as we're usually limited to one or two teams per squad.
Generally speaking, the ROs will be finishing their match on Friday, so personnel available for check-in/weighing/PF (chrono) will be limited and timelines usually slide.