Bout 15 minutes. Only reason I say low RPM till it gets pressure is because slants are difficult to prime the oil pump. Without a prime, there can be air trapped. If it hangs up and does not get oil pressure in no more than 20 seconds, if you're at lower RPM, you've done no damage. But once it gets pressure, zing in on up to 2500-3500. I usually go on up to 4000 varying between 2500-4000. It's all about oil splash. That's the only way the lifters are lubed until it gets pressure. The lifters don't see any pressurized oil, all they get is dripping off the pushrods, and it doesn't get there for a few seconds.