On the 737s, well, at least on the classic, you will get blinking ALIGN lights and a scratchpad message (VERIFY POSITION) if the position you enter is more than 4NM from the last known position on normally working IRUs. The IRUs also do an internal comparison test with sensed latitude and prompt with the scratchpad message ENTER IRS POSITION if the position you entered doesn't fit. Unfortunately the ALIGN lights blink as well if you do not enter any position on first align or if airplane movement was detected during alignment. If alignemt wasn't complete and you move the airplane you will get the flashing ALIGN lights, scratchpad message IRS MOTION and a full realing process will start automaticly.
Our SOPs require us to do at least a quick align on each turnaround and preferrably a full realign if time permits, which it usually does, min turnaround time is 30 minutes. Both on the classic (non GPS) and on the NG (all GPS equipped).