If I understand everything correctly, you've got something like 48 matches at ~50 minutes apiece. And rather than the MAXIMUM amount of time (which could be infinite for all we know), I'm going to tell you the minimum.
So we've got 48 * 50 = 2400 minutes. 2400 minutes / 60 minutes = 40 hours.
Granted this is your total time, and when matches are going on at the same time, this is compacted the number of rounds.
EDIT: RIP Croatia. Also, if you're assuming everyone starts on time (never), everyone finishes on time (never), all the equivalent rounds in both brackets occur simultaneously, AND that the two brackets are both running at the same time, then you just multiply 50 mins * the number of rounds. So about 50*8 = 400 minutes or just shy of 7 hours. This doesn't count any break time or technical difficulties or anything extraneous.