Confusion about granularity vs. decay rate

In #1155620: D7 Version very different, you state:

Difference between granularity and decay rates:
Granularity = how often do we calculate the values (=how accurate is the modelling, think of this as cron time of the field)
Decay rate = the half-life of a value

This is still not terribly clear to me.

Let's say I have granularity set to 6 hours and Decay Rate set to 12 hours, and cron runs every 5 minutes. Node A currently has a heat of 100. How much heat will it have after 6 and 12 hours?

Does it matter when the node got the heat? Say, 2 minutes before the decay run, it got a bump of 10 points. Is that dropped to 5 only two minutes later?