HalHoff: You have to complete your round by the time the invisible clock ( at least on mobile anyway) strikes the tournament ending time. Those times also vary throughout the day depending on when the tourney is created.
Variable times to finish are only possible in CC tournaments and in RGs and Brackets.
Isn't there a clock running down visible when you select the tourney, just before entering the game? (On PC, there is).
WGT tournaments (weeklies, montlies) always finish at 11:59 pm P(D)T (San Francisco time).