I'm not sure HTTPS is an option for this as it requires accurate time/date for encryption. Maybe the RTC could be valid, but I'm not sure it handles different time zones well and it might have lost time anyways.
HTTP support is implemented by an EFI driver, so it's up to the UEFI to provide it in a way that works. The UEFI spec allows both HTTP and HTTPS URLs.
I would classify something that doesn't care what century it's booting into as an unimportant device. If the clock is off by a lot, it still should not boot over network.