Rick left the Hospital on ZA+60 (after several weeks (21 days is several weeks), though there would have been a functioning infrastructure even during the initial outbreak. Once panic, and breakdowns occurred, the Hospital would go automatically to generator (usually a 2 week supply - could be more if chaos and the hospital was abandoned - less resources used) - Shane visits Rick 2 weeks into his coma, Shane comes again, blocked RicksRick's (ZA+46) room when the military showed up and started shooting. So 1 week after ShanesShane's attempt to block his door he walked out of the hospital in ~West Point, GA (90 miles from Atlanta).
Rick met up with Lori ZA+62,on ZA+62; on ZA+70 Lori asks for a preggerspregnancy test. ZA+84 is the last episode seasonin Season 2.
Season 3, episode 1 Lori is due any day (8 months have passed) - so if RicksRick is the babiesbaby's daddy (ZA+/-329), if Shane is the babiesbaby's daddy - (less than 8 months have passed (why Rick is not too happy - don't need to be math geniousgenius here)) ZA-322 (before RicksRick's arrival at the quarry and whoppiewhoopie.)
nowNow that is all in the sense that Lori is going full term and is not pre-mature.