what do the instructions say to do? most drop ins like that need to be glued down. the ones i used to install came with a small tube of adhesive. because i couldn't come back the next day i used to either glue them and set something on top of them so they didn't move while i connected the drain and waterlines or i would connect everything and then glue them down. there was enough give that i could lift them up slightly and squirt the adhesive under the edge. in your case i would glue it down and then connect it the next day.