Thanks for the question.
Register shifts are (currently) only meant for 1) tracking your cash float 2) totalling your payments at the end of the day. A few customers I have spoken with use Time Scheduling apps off of the App Store to track their employee shifts. That would be the best workaround for now.
Staffy (https://apps.shopify.com/staffy) is the solution you're looking for. That's what we do