Unfortunately, there's no one single answer, because there's a long list of factors that influence relubrication frequency.
Generally, the smaller the bearing and faster the speed, the less frequent the interval for relubrication with grease. Larger, slower bearings require more frequent relubrication.
Different types of bearings require different relubrication frequencies:
1. Radial ball = base interval
2. Cylindrical roller = 5 times as frequent
3. Thrust-ball and roller = 10 times as frequent