In your spare time
Reading before bed is great and on weekends when you have some time. If you're really busy during the week then trying to squeeze it in is not effective (from my experience). Especially when you want to read business books, self-help, magazines, etc because you need to be able to focus without any interruptions and restraints.
Try to do it on weekends and before bed. Or, if you want to step it up, go to bed earlier, wake up earlier and read right after breakfast before you do any work.