If i only change certain parts of the screen, will it do a full refresh?

I am thinking of getting the Inky Impressions or Inky wHAT, but I am concerned about the refresh rates - it’s advertised as taking up to 40s and 25s respectively.

If I were to make a ‘clock’ that updates every minute (just the mins part of the screen, as it’s a clock), would this trigger a full screen refresh or just the parts changing? Will such a small change also cause a 40 - 25s refresh (making the screen flicker/unreadable)?

Could you also suggest a large screen for a clock and dashboard display? I want it to be ideally >= 5inches, and it will refresh for the clock every 1 minute. The rest of the data e.g. weather will not change.

Thanks!