I have a second (Excel) spreadsheet for single (or two) summit activations.
It has a separate page for all the summits for each region (G/LD, G/NP, etc) that I activate regularly. It has drive times (based on Google Maps or actuals) and ascent times (based on OS Maps app or actuals) [although some never-activated summit entries are still blank].
I put in my departure time and it calculates on-summit arrival time (for posting my SOTA alerts), parking duration (useful for parking charges) and total away-time (useful for sweet-talking my wife about when due home).
It’s been pretty reliable and notwithstanding unforeseen events (like road closures) I’m usually on summit within +/- 15 minutes of my alert times.