if you are on a 33 day cycle, honestly I'd wait until day 34 or 35, of even a few days more if you can stand it. I just think they are expensive to waste, but if you have a few and want to go for it, just make sure to use your first morning urine and if you are pg, you might have enough of the hormone to detect.
if you are looking for a recommendation for a test, I loved first response. I used it for both pregnancies. with my first, we were surprised (weren't trying yet) and I took a test I would say 3 days late (normally a 26 day cycle, so day 29). with my 2nd pregnancy, I knew I was pg. I never have heartburn, except when I was pg with my first, and about 4 or 5 days before my period was due, I had heartburn. I had a test in the house so went ahead and did it the next morning and sure enough, positive. now, I ended up with twins so not sure if the added hormones helped get the positive so early.
hope you get the answer you want!