This is a question that comes up often, and I try not to sound like a used car salesman when I tell people that there really is not a “perfect” time to visit the interior weather or fishing-wise. Some lakes fish best early season and begin to taper off somewhat quickly, while others take a while to get going and seem to have a prolonged period of consistent fishing.
Elevation, depth and amount of sun or shade that a lake receives are just a few contributing factors to the timing of each fishery. There is no way to tell what the weather will do, you can have shorts weather in April and you can have a hail storm in June. There are lakes that seem to peak when everything else gets past ideal temperatures. Tunkwa Lake is a prime example of this, if I were to plan a visit there I would pick late July into August to fish their “bomber” chironomid hatch.