Unless I'm crazy......you don't need an alignment if it's only the PML. I did shackles and AAL, and had to wait for the front spacers...and I did not need the alignment until I did the front spacers.
The PML causes the camber on the tires to tilt in. It depends on how much driving you do, but the sooner the better. Make sure it is someone who knows how to do an alignment and not reset it to stock settings as well.