After the first couple couple shots, I wait about 2-4 minutes between shots depending on barrel contour, cartridge, temperature and wind... what ever it takes to keep the bbl temp the same, which is just "barely" warm to "cool" to the touch.
Throat errosion is the worst enemy with heating them up excessively. Groups may change as tolerances change and length of time the cartridge dwells is the chamber before firing, a "good" chronograph will indicate how bbl temp is affecting velocity and thus trajectory, also harmonics will change if this occurs. Alot can go on if things aren't kept consistant.
When I shoot steel at long range, I'll always shoot groups like I would hunting to see how the rifle performs in that situation. If I am making a drop chart, I keep all things consistant, as I do on load development.
Noting the cold shot impact is very important, as well as point of impact shifts.
I only start making a chart, load development, or head out hunting with at least 3 rounds through the barrel to foul it first, some guns take 5... no oil in the bore after that, just tape on the muzzle when hunting.
Some loads toward maximum load are more sensitive to bbl heating than others, a good chrono will tell you what's happening in the chamber though.