I just tried the above 45 days cron example and Jenkins max time is about 30/31 days so...

Uhm, I have not found any issues about this. It seems "This field follows the syntax of cron (with minor differences)" this is one of the minor differences. Maybe someone else can come up with some other idea. Other than that, you could just use some flag token and then check whether since the previous build and the current one there was already 50 days difference, by running that job on nightly basis and if so then trigger either another job with those details.
Cheers