My general advice is to buy fast lane plus no matter when you go, busiest six flags park period, never been there where I didn"t absolutely need it. I have found that both thursday and friday from open until about 2 P.M. are the slowest, even with FLP it:s nuts, after 3 P.M., fuhgeddaboudit. All of our (U.S ) holidays are always slammed there. I have tried spring, U.S. holidays, summer, fall, Canadian holidays and every weekday, ect. I am not local, but live just across the border in NY and go frequently. I go to Cedar point more often and this place is just busier always, just no relief of crowds ever. All of that being said, great park in a great city. FLP here is very much like Kings Island as the FLP lines are generally short , less Alpen fury (average of 45 minute FLP wait), everything else is 5 to15 minute wait. My best park attack is to get your FLP first thing as the line just for the FLP can be 30 minutes and you can only purchase from 3 locations in the park (Main entrance, by Leviathan and a little kiosk back near Yukon Striker) the latter 2 do not open at gate drop, only after FLP can be used. Hit up Alpen Futy as the lines will never get shorter, ever. Then go either to Yukon Striker and behemoth (there are way more rides back there), or go marathon Leviathan. If you want to ride the non FLP rides, hit them up first, as gaurdians and thunder run, ect., the lines just get insane. This park is really awesome and I hope you have a great trip. If you have time , the city in itself is awesome, so much to enjoy.