Time between dosing and UV exposure

So I’m currently on holiday in hot weather, UV 8+ most days. I’ve started dosing 250mcg every second day. My question is, if I pin in the morning and then don’t get UV exposure that day, is the dose essentially wasted? Does it only tend to work if you pin on days you go out in the sun? I can’t find any research on how long it stays effective in your system for. Would you just continue dosing every second day on holiday and not worrying about when exactly the sun exposure is? Or do you time dosing for when you know you’ll be out in the sun?