<human>: A little background.  I have worked at this job for almost 1 1/2 years.  My job requires 24/7 coverage on site and I was thrown into the busiest and most critical shift due to my experience with the critical work performed.  The way our schedule works out, I hired in expecting 36 hours on week and 48 hours the next, netting 8 hours of overtime a pay period (every 2 weeks), however, the way the set up the work weeks it cut my pay down to two 42 hour work weeks, taking away around $1,500-2,000 a year less than I was expecting (and promised, albeit verbally.)  Of course, management has no recollection of the guarantee.  

Recently they started to require only licensed people can do perform the work that I currently do on my shift.  The only other licensed guy put in his two week notice today.  This leaves me as the only qualified person to do this work and it would cost the company thousands to bring in a contractor to do the work.  

Performance evaluations are coming up at the end of February and I'm not sure if I should ask for a raise now with the new requirements just taking effect, or if I should wait for the performance evaluation and try to negotiate one then?

Could you distill the essence of the text into 1-3 sentences?
<bot>: I'm the only qualified person to perform a task at work, should I ask for a raise now, wait for my performance evaluation, or blow it off altogether?