Three weeks should be more than enough, unless the tiles are really big, or you live in a very humid climate.
More specifics will help others suggest possible solutions.
How big are the tiles?
You are firing to 1080, I'm guessing that is Celsius?
What kind of kiln and kiln controller are you using?
Are you doing any type of Candling?
How exactly are you arranging the tiles?
For my classroom kiln, I do a relatively slow firing, to make sure those student projects (Of questionable construction) survive. My program is 50 degrees F until 200 F. Hold for four hours. Then up to 900 F and hold for an hour. Finally up to Cone 04. With this program, I've had very few issues.
I've never made tiles (Other than glaze test tiles), but I've fired plenty of slab constructed items, boxes, relief sculptures, etc. I have had issues with some of them cracking or exploding, which I have solved by firing boxes upside down, or on stilts. I've fired really large slabs on coils to avoid stress build up during expansion and contraction. Some use a layer of sand for the same reason.
Best of luck!
- dror likes this