These are the "signs" I look for in line "movement" to indicate a bite :
Single, quick jump of the line
Line starts moving off to one side or the other
Line straightens out on the retrieve & feels like you have a large leaf stuck on jig
Line suddenly goes completely slack (& you know bait can't be on bottom)
ANYTIME one of these things happens ... set the hook IMMEDIATELY !! Yes, unfortunately you will get hung up every now & then, like when you mistake the jig bouncing off a limb as a bite
But, that's all part of the learning curve, and those instances will decline with time/experience. BUT, you will also have a higher percentage of hookups, too !!
My best strategy for early or late day shallow water fish, is to put the jig down & fish a 1/32 or 1/16oz marabou Roadrunner !! They're more of a straight cast/retrieve (at a moderate speed) type of lure, and the blade helps keep it "suspended" at a shallower depth. I never worry about the fish not being able to "catch up to" my bait ... because they can see or sense it coming, long before it gets within their strike zone. They're ambush predators, not slash/dash predators or long range chase predators ... so they're quite aware of what's going on around them, and if they're interested or curious about something coming their way, they'll position themselves to intercept it. A lighter jig, and/or use of a float are certainly viable options to consider.
Crappie prefer shade ... and they'll generally find it, whether it's from obstacles above the water or below the water ... and even the clarity of the water. They will also use depth in open water, as "shade".
I really don't know if there's a strike window as it pertains to retrieve speed, since they seem to easily catch a jig or crankbait running at 1-2mph. But, yeah ... different presentation methods do usually call for different speeds of the bait. But, even then, slowing down or speeding up from the "normal" speed of the bait can be more productive ... it just depends on a bunch of different factors, many of which we have no control over.
Fish are cold blooded, so they're the same temp as the surrounding water. That doesn't prevent them from moving as fast as they would in warmer water ... it just slows down their metabolism, so they don't need to eat as often. I've caught fish from Dec-Feb, with water temps in the 40's, on the same jigs, retrieved at the same speed as when the water temps were in the 70's & 80's.
Note : fish can see better/father in colder water.