Using this userscript I made : git.kaki87.net/KaKi87/userscripts/protonmailWithoutAnnoyances

ProtonMail allows scheduling and snoozing messages for free at preset times, e.g. tomorrow, next Monday, this weekend, etc., and always at 8, but makes people pay to choose a customized date and time.

I had a hunch that this restriction might only be implemented client-side, so I tried modifying the value in DevTools for the first time, and I couldn't believe it : that worked !

So, in order to automate this, I created a userscript that replaces the button press handler for the "custom" option, then lets you input whatever value you need, e.g. (next) Wednesday, (in) 30 minutes, (today at) 8 PM, Thursday at 7 (AM), etc.

Then, it lets the app believe that we're gonna schedule using the tomorrow preset, until it intercepts the request and swaps the time value with the user's choice.

Enjoy !