[MENTION=13244]Tom[/MENTION], the best way to measure it is as follows: (You can do this for all Hearthstone tournaments in the future). Always allocate 60 mins to a game. For Saturday night you are playing the groups of 4.
Detailing it in full here as I am copying this to the tournament website as well

:
Groups of 4 Schedule
Matches will be played on the 25th.
Each group has brackets with the titles of A, B, C, F, G. (It is the letter next to the bracket).
Bracket A and B will be from 17:00-18:00.
Bracket C and F will be from 18:00-19:00.
Bracket G will be from 19:00-20:00.
Single Elimination Rounds
Matches will be played on the 26th.
Round 1 will be from 17:00-18:00
Round 2 will be from 18:00-19:00
Top semifinal will be from 19:00-20:00
Bottom semifinal will be from 20:00-21:00
Finals will be from 21:00-22:00
Opponents must pitch within 15 minutes of the start of the game, or you may claim a default win.