Wrongly detected date (on misuse of 'at')

[Mayerch1]

The string every other year at 26th march is wrongly detected as containing BYHOUR=26

It is caused by the regex RE_AT_TIME which is expanding to

at\s(?P<hour>\d{1,2}):?(?P<minute>\d{2})?\s?(?P<mod>am?|pm?)?(o\'?clock)?

I'd propose to use the following look-ahead, to ensure the number is not followed by st, nd or th. (?=[^(st|nd|th|0-9)])

So the complete RE_TIME Regex would look like follows

r'(?P<hour>\d{1,2})(?=[^(st|nd|th|0-9)]):?(?P<minute>\d{2})?\s?(?P<mod>am?|pm?)?(o\'?clock)?'

All given unit tests pass the regex modification.

Before I create a pull request on it, is this modified behaviour even desired? The English language doesn't use at to specify days, but it's nevertheless (wrongly) used by foreign speakers.

The big issue I see is, that similiar strings like every other year at 2nd july will not cause errors, but will result in an rrule, which repeats on 2nd july at 2am.