Going to make my first trip to tongue river reservoir sometime in may or june, hoping somebody could help what time would be better,thanks
IMO, the fishing at TRR doesn't really turn on until the water warms up, which takes a long time with the reservoir's canyon-like nature and depths involved. During the runoff, its tough as many of the fish are in the shallows back into and beyond the old treeline (developed before the dam/reservoir was raised in the 90s) where it is difficult to get to them.
Don't know where you are located at, but if it were me, I find better early fishing elsewhere. For example, Peck can be excellent with the eyes, smallies and pike hungry, and the sun and bugs not yet bad.
Of course the camping at TRR can be very nice too that time of year. Also, don't forget below the dam in the river which has a nice campground and a little-known trout fishery in the first couple miles downstream.
My .02s.