The only way to find out is to keep shooting it until it starts to malfunction. Most of the polymer pistols don't need much lubrication, because the slide rails are so short. Glocks are the shortest. They basically build up a certain amount of crud, then they self-clean and maintain that level of crud from there on out. The small contact area between the slide and rails allows the gun to work without any lube. I don't do it as a torture test or to brag, but I haven't cleaned or lubed my G19 in about 800 rds, or so, just because 1. I'm lazy and 2. it doesn't seem to make any difference.
Some polymers, like the Steyr and Sig Pro have nearly full length rails, so they need to be lubed more often.
Some polymers, like the Steyr and Sig Pro have nearly full length rails, so they need to be lubed more often.