Early morning or late evening its always empty very few people workingout it makes it ideal for a good workout...
I know this question is a little old but there is a new planet fitness app you can download as a member that includes a "crowd meter". This will allow you to know how busy the gym gets throughout the day. Really cool new feature! That way you get in when the gym is just right.
I find it less busy around 6 in the morning. That's when I go and there is around maybe 10 people there.
About 11:00 am thru 12:00 pm
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