On a single speed bike it's very reasonable to run chains fully up to 1% (true) stretch. That's 1/8th inch over 12 inches measured pin to pin under enough tension to pull out any slack.
In fact that was in historically the guideline for derailleur chains, and has only recently (my time frame, maybe not yours) been reduced to the current 1/2% beasuse of smaller sprockets and index shifting.
On a single speed, the longer wrap, lower tension (because of larger rear sprocket) and 180 degree wrap, mean slower sprocket wear. Odds are that you could run 5 chains, each to as much as 2% stretch before noticing any issues.
Last edited by FBinNY; 09-16-22 at 09:09 PM.