How to calculate payoff & breakeven for legs with different expiry?

I see on sensibull suppose, I add 18000 & 18100 call then payoff given at 18400 lets say is total of pnl of 1st leg & 2nd leg. But when I change expiry of one of these leg. it’s entierly different then just sum of two legs profit.
How does one calculate payoff for legs with different expiry ?