playing strength change during the day?!

when I have just woken up in the morning and I have slept around 7-8 hours I feel like it is easier to solve tactics

but later in the evening and I have been to work I feel like I am not that strong.

How many rating points( playing strength) can someone drop during a day.

I guess it is more than 50 rating points. being able to spot tactics is very important.

I typically play at about 1700 strength, OTB.

If I attempt to play too early in the morning, or too late at night, I tend to forget that the horsey moves in an "L", and move the pawns like checkers.

I believe it may have something to do with a players STYLE, & of course different players react different to various situations. But on average is a player more tactical/dynamic or more strategical/positional? I believe most positional players Capablanca, Karpov, etc. would be more consistent whether they play in the morning or night & more combinative players Alekhine, Kasparov would play better early after rest because of the mental energy needed to calculate variations more acurately. Positional/strategic players rely more on deep strategic feel, understanding & long term planning to grind their opponents down & squeeze them like a python (as Roman Dzinzichashvili would put it). Tactical/combinative use more detailed analysis of variations & feel more compelled to split their opponents chess position in pieces with a tactical sledgehammer, that requires more intense short term energy whereas longer term startegic play may require mental energy spread out over a longer period, in moderation. Just my personal observations. Damon

Since you are not a machine, being tired or bored or having just eaten (so your blood is around the intestines instead of the brain) will make a difference.

You want to be careful not to read too much into observations such as this.  Mental alertness/fatigue DOES tie directly into how well you see tactics under time pressure and if you are playing really fast games, this could swing your performance up and down by huge deltas.   Visualization errors are also bound to happen under fatigue.