Other than the stuff about dams etc, I don't find dawn heralding anything special in terms of water level in rivers, good for fishing though
On the Tummel in Perthshire, major tributary of the mighty Tay, dawn is generally when the level is at it's highest as the dam at Pitlochry usually lets some water out first thing to move salmon and grilse up to the ladder for the tourists to oggle at from the observation station later in the day.
I guess snow melt in the arctic/subarctic north may slow during the night, but as to influence on levels, that would depend how far down stream of the melt one was. More than 30-35miles and I could see that not really making much difference as you'd be ahead of the melt delay, plus there'd be more local influences to consider. In the arctic/subarctic north one would want to be early or quite late in the season to take advantage of lower river levels. Through the summer months the water tends to be at it highest.
In scotland, where I've done most of my fording wading and fishing, I keep quite a close watch on river levels because I'm usually fishing, and perhaps looking to cross somewhere, that and the fish tend to run just as the water rises and again when it drops.
Some rivers, on skye for example, can go from raging torrent to gentle stream within an hour of the rain stopping, due to the limited reach from source to the sea, a max of around 6 miles because one is never anywhere on the island more than that from the coast, plus skye has a really steep run off too. Unless they're having a massive thaw on the skye hills, snow melt has only a small influence as the hills hold limited amounts. Rain, and the seemingly endless deluge has by far the biggest effect on levels.
Rivers local to me are similar but tend to drain larger areas and while the ground is steep, rising and lowering is a more gradual slower affair, this is the western watershed which is very short compared with that on the east, the western water shed on local rivers is 20 miles maximum with 10 miles being more typical. On the east, the Spey and Tay, in particular, the sources are more or less on the west-coast or not far then crossing the width of the whole country, meaning the rivers can rise and fall due to influences many many miles away. Anywhere half way down those rivers one is looking for a bridge or a boat, to get across.
The biggest problems I've had with fording running water has been on tiny streams that turn into impassable obstacles in heavy rain, I've gone up the hill fishing forded up to my ankles and found the same stream impassable on my return. I reckon of all the things we get up to in the great outdoors, river/stream crossing has to be about the most hazardous of ventures. It doesn't take much to wash you off your feet, and once in it can be quite a task to get back out. Most don't make it.