Clocks are a key tool of the game. A clock is a circle split into a multiple of 2 segments (between 4-12 generally). These can represent anything that takes time or resources. Such as guards finding the party or discovering the location of the crypts. The clock completes when every segment is filled.
When a clock is filled by a skill check:
Crit is 4 segments
Great is 3 segments
Pass is 2 segments
Fail is 1 segment