To test it, I opened a sheet more than 60 times. On open, there were running some Google App script code. Each run took around 1 second. In my case, it ran more than 60 times and is still running if I open that particular Google Sheet. I think the execution limit might be like:

Execute it as many times as you want till the app script cumulative run time is not exceeding 90 minutes in a 24 hour time period. 90 minutes means 5400 seconds. To validate it, I can't test the 5400 second limit manually. Note: I have a free Google account.