[eluser]Aken[/eluser]
ClaudioX, I see that you added a lot more validation as far as date and time ranges. Ignoring some of the small bugs still in it, I wouldn't recommend such a regex when it comes to validating dates, because 99% of the time you'll still need to verify things like if the date is within a set timeframe, if it actually is a leap year so February 29th is acceptable, etc. I realize mine is incredibly basic and only verifies the number pattern, but I think because of the other sanitizing that needs to be done, that's the most you'd want to validate against when it comes to user input.
I might spruce up your regex a bit and post it here regardless, just as like a tutorial or "in case you want it" type thing. If you'd like to know how you can fix your regex a bit, just let me know and I'd be happy to share some suggestions.