They will let you know today that you have short call reserve tomorrow.

The only time I have held LCR I sure got escalated. My buddies, both FO and CA have always been escalated both times every month they've been on LCR.

For whatever its worth, 2 weeks of LCR is better than nothing, but LCR is definately not as good as it sounded at first. Specially if the 2 weeks that you are actually on LCR you will be used first as soon as some flying pops up...