Hey Jace,
in my spindle’s manual (a 6,000–24,000 rpm 2.2 kW water-cooled spindle), it says:
10.2 Spindle run-in
A cold spindle must always be run in thoroughly before it is put into operation in order to gently bring the bearings up to operating temperature. The stated run-in times are to be doubled if the spindle has not been used for more than a week, is brand new, or the bearing has been changed.
When running in, the speed should be set to the minimum (6000 rpm) and maintained for at least 1 minute. The speed can then be increased in steps of 6000 rpm and must be maintained for a further minute each time. The speed is gradually increased until the desired operating speed is reached.