More flexible alerts setup

Often times I want to have an alert at a specific time the previous day, or e.g. a few days before an event (in case I need to make a booking before the agreed meeting).

As I only could provide an exact numerical value for minutes/hours, when setting an alert up, I have to calculate hours manually and use something like "18h before", instead of a more reasonable "at 11:00 a day before".

UX isn't great at its least.