Clarify options for 'offset' on date field filters

Currently it says

An offset from the current time such as "+1 day" or "-2 hours -30 minutes"

I guess the available options are what some php function allows, like strtotime(), see here:
http://php.net/manual/de/datetime.formats.relative.php

If that is the case, it would be nice to have that explained, maybe with a link even.

But the above link does not mention the plurals of hour and minute, so i'm not sure.
And i have quite no idea on where to look in the code to find the relevant parts.

PS:
Maybe there's also a typo?
An offset from the current time such as "+1 day" or "-2 hours -30 minutes"
should maybe be
An offset from the current time such as "+1 day" or "-2 hours" or "-30 minutes"
Or is "-2 hours -30 minutes" trying to indicate that calculations can be done too? ( = -1.5 hours)?
That would be a nonsense example ;-)