You're under the southern region supplmental.
First go here and download the National Master Agreement and the Southern region.
UPS and UPS Freight Agreements, 2018 – 2023
They are your contracts
Personally I think the Southern has the worst language for PT schedules.
But..
You are being ordered to report to work at a certain time and Article 17 of the NMA say that you should be paid.
View attachment 284218
Speak with other employees tomorrow (not supervisors) and find out what teamster local you are. Its should be a # like I am teamster local 542. Once you know this info we will be able to help you more.