"Rule" is a stretch, but I know for credit spreads some folks recommend closing immediately if you can keep 50% of the premium. The idea being if you open a 45 DTE spread and market moves dramatically in your favor, and you can close with 50% profit after just 10 days, now you can go and reinvest that margin instead of waiting another 35 days.
What I'm noodling on is how (or if) you'd apply this rule to debit spreads. I recently opened a few call debit spreads because I felt bullish on some stocks but they were not volatile enough to give a good credit premium. Now five days later the market is above my long strike! But closing now only gives a small fraction of possible profit ($190 out of $650).
TLDR: what's the earliest you would consider closing a debit spread? Or if no limit, what % of possible profit would you want to capture before you'd close and pay for the remaining extrinsic?