Remember that it expires in 5 years on your birthday and they don't remind you. We found out the hard way. It is much easier to get re-approved if you reapply before it expires.
The amount of time it takes to get initially approved depends on how busy they are. When we had to get ours renewed it took a long time because of the government shutdown earlier this year. Also find out if your credit card covers the cost because some of them do. I know hubby's AMEX covered his cost and we just had to pay for mine.