pumpTimers

Runs the timers a script set with app.setInterval or app.setTimeOut that are due, and returns how long to wait before the next one, or null when none is waiting.

The timers run on the runner's clock, the one the budgets use, and nowMillis is not read: a timer fires after its delay, counted from the moment a script set it, whatever time base the caller pumps with (#367). Nothing runs on its own: a document cannot take the thread from the host.