A/C Recharge

1988 XJ that had a/c junk yard components installed. Used Green R134a compatible seals and new dryer/reciever. Drain oil from compressor and put in R134a compatible synthetic refrigerant oil.

What would happen if I didn't have time to evacuate the system and just charged with R134a?

If you don't put the system into a vacuum, you will have air in the system. The problem is, if you don't pull the air out, you can't get a full charge of r134. And the r134/air mixture doesn't do the whole turn to liquid, then evaporate, then turn to liquid thing as well as pure r134.
So the short answer is it won't cool worth squat.
Pay some one to do it for you. We only charge $60.00 labor for AC service, I can't imagine it would be too much more, even in California. And we check for leaks when we're done.