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Depends on the kind of machine and how old it is. With video poker machines (both older and newer), hold buttons have tactile feedback so if there's a problem with an unresponsive button, it usually can be fixed by changing out one small plastic part -- something which would take just a few minutes. In contrast, many newer slot machines use a touch panel or "virtual button deck" for a player to set the amount they want to bet and if that's not working properly, a slot tech would first need to see whether or not the sensor needs replacement, and then perform a recalibration. Either way, that usually takes a lot longer than replacing a plastic part on a video poker machine.

Perhaps most importantly, if a machine is not working properly, people will catch on sooner or later and eventually stop playing until it gets fixed. The longer a machine stays unplayed, the less action it gets and the less revenue the casino makes. So it's in the casino's best interest to have enough staff on hand to keep all their games well-maintained.