The people at "311" say that once you pay for time at a muni-meter you cannot use the remaining time at any other location--anywhere--even on the same block, but they cannot provide a citation to that effect. Last Sunday's New York Time's Metropolitan section, page 3, has a quote from a chief police spokesman saying you can indeed use the remaining time at another muni-meter location--but only on the SAME side of the street!
Speeding / Traffic Ticket Lawyer
I blogged about this very issue just a few months ago. Here is the link. http://888redlight.wordpress.com/2009/04/13/nyc-muni-meter-tip/