Oil should be checked allowing time for it to drain back into the crankcase. My preference is check it first thing in the morning when I check tires. On some engines, especially with a long dipstick tube, you will get a better reading if you remove the stick, wipe it dry, and wait a few minutes to re-insert. I pull the dipstick, check the tires, and then check the oil.
Logically, the reason a dipstick has a low (or add) mark and a full mark is to define absolute minimum and maximum levels. Also, there is really no significant change in oil volume due to temperature variations. Mine reads the same level regardless of ambient or engine temperature.
Since I do my own oil changes, I let it drain for an hour or so (from a fully warmed up state). Oil is still dripping after about 20-30 minutes, which is indicative that some is still working its way through the block back to the pan.
