Yeah INS doesn't have a stardate so you can be flexible with when it is set. I like to think INS happens after the Dominion War ends.
I think it was meant to be set in the seventh season of DS9. Worf became Federation Ambassador on Kronos when DS9 ended, in Insurrection he is wearing a Starfleet uniform and Picard orders him to delay his return to DS9.
It really doesn't make any sense for the Enterprise to go on archeological research while the rest of the fleet was fighting the Dominion ... but the producers were afraid that the average moviegoer would be too stupid to understand that there was a war going on. The strange thing is that the war is being referenced in the movie several times, it could just as well have been a major part of it. Three lines of explanation for those who have never seen DS9 would have been enough. The biggest missed opportunity in Star Trek ever!