You will want to finish the premed classes before you consider taking the MCAT. So your timeline will depend on how many classes you can take per semester. If you're working full-time, I would guess that you wouldn't want to take more than 2 classes per semester, and even that might be tough when you factor in the requisite lab time. But if you could manage the two, a good plan would go something like:
Semester 1-Intro Bio 1, Gen Chem 1 (with labs)
Semester 2-Intro Bio 2, Gen Chem 2 (with labs)
Semester 3-Intro Physics 1, Orgo 1 (with labs)
Semester 4-Intro Physics 2, Orgo 2 (with labs)
I wouldn't really suggest taking the MCAT until after you finish the courses. So if you were to start this fall, you would finish in the spring of 2005, and I would recommend taking the MCAT that August, after taking a prep course.