It's of big importance to watch the green speed of each game, upper right corner once you're on the green.
Green speeds are named in the FAQ, their relative speeds are 90% (slow), 100% (standard), 110 / 120...% and so forth.
As a beginner, you may go through the starting tiers quite quickly => green speed changes.
OTOH, in rated multiplayer games, the green speed will be set automatically according to the highest tier in the game. In practice games, it may be set ad libitum by the inviting person.