Originally Posted by Trek'n Teresa
Hello bicycling friends,
...
When is the recommended time or miles to replace a chain?
The reason I ask is I thought I heard a bike shop owner
suggest replacing chain at 500 miles or 1000 miles ...
but I am not sure exactly which one he said?
...
Thanks in advance,
Trek'n Teresa

Sounds like that owner wanted to sell some chains. Probably the 40 or 50 dollar ones to boot.
The more force you put on a chain the more it stretches. Racers can go a good 2000 miles on most chains. My suggestion is to measure it every so often with the 12 links=12 inches method or the park chain tool and keep it clean. Replace when stretched, when there is excessive play, or skipping or poor functioning.