Talking B737-345 here.
On turnarounds, I place the IRS to align, and enter the Ppos, and leave them there until the checks for the next flight. By doing this, if you look at the STS page on the IRS on the overhead panel, it displays 7 for 3 mins, and then counts down to 0. Now I presume this is it in the process of a full align, but you have the advantage that if the aircraft is to be towed for any reason you can bung it back to NAV so you don't lose your align. Hence you get a full align each time, but with a bit of flexability!
Coug..............h
ps I'm only guessing that its doing that!