Will my work be entered twice if I retry?
No. Each item carries an identifier the server records before doing the work, so a repeat is recognized rather than repeated.
From the guide Working offline.
Why nothing gets entered twice
Each held item carries an identifier made once on your phone. The server records that identifier before it does the work, so if the answer is lost on the way back and your phone sends it again, the second copy is recognized and the work is not repeated. A repair request made in a basement arrives once, not twice.
The time recorded is when you did it, not when it sent. A clock-out taken at 5:02 and delivered at 6:40 is a 5:02 clock-out.
Read the whole guide: Working offline