Due to average 120 days OPT Processing time, your OPT Requested start date could be beyond the Approval Date. So, will you lose number of days on OPT?
See this example shared by a user.
There you have it.
Just a piece of quick information about the start and end date for EAD card in case you get approval beyond your requested start date:
My requested start date (written in OPT I20): Aug 19, 2019
My requested end date (written in OPT I20): Aug 18, 2020
OPT approval date: Sep 3, 2019
Actual start date (form SEVP account): Sep 3, 2019
Actual end date (form SEVP account): Sep 2, 2020