Time between shots at the range depend on many factors...how much powder are you burning, ambient temp, barrel weight/thickness, and velocity of the cartridge. When shooting calibers that generate very high velocity, time between shots needs to be extended.
Most of us at the range shooting varmint calibers use either a sporter or varmint weight barrel. Common sense dictates that the sporter will heat up much faster, thereby requiring more time between shots so as not to overheat the barrel causing throat erosion. Almost all my varmint rifles wear varmint weight barrels, and I've found that in cool temps of about 35*-45*, with cases of about 25~grs capacity or so, a time interval of about one minute between shots works okay. It takes a bit more wait time with a sporter weight barrel.
If you were shooting a sporter weight barrel chambered in something like a .338 Ultra Mag that burns in excess of 100 grains of powder at a wack, you'd want to wait much longer, as burning over 100 grains of powder in a single shot really heats up a barrel pronto!
BUT.....you'll want to use this as a guideline only. Before taking the next shot, hold your hand against the barrel just ahead of the chamber and feel the heat....if you can't hold your hand against it, it's about 160*, and too hot to continue shooting (if you want to save that throat). Longer periods if you can feel real heat and not just a warm feeling to the steel.
In the end, you will be the determining factor of how long to wait between shots. A huge dose of common sense is required here, along with a bit of experience over time. After a few trips to the range, you'll have it figured out. Just keep the heat down to a minimum and that barrel will treat you well. Just remember: Heat is your barrels worst enemy.
