The clock starts counting upon the completion of the crime. There are exceptions as I explained previously; for example, if your crime involves conspiracy with another person, then all future communications with or actions in consort with that person in furtherance of your crime resets the clock. To give an example, if you collude with someone in accounting to defraud your company and have them sign false financial statements to cover it up, the clock is reset upon each signature they make or each time you ask.

Some district courts have held that the statute of limitations can be tolled while the suspect is actively evading law enforcement even if they remain within their jurisdiction; some haven't.

I'm in England, but I'm talking about United States Federal Law.