I want to run cron job every night at 1am and after that every 3 hours from morning 10am-6pm only.
0 1,10-18/3 * * *
Is this the correct format?
Personally I would simple spell out the hours rather than using the step. Even though your syntax seems correct
10-18/3 looks awkward to me.
0 1,10,13,16 * * * command
Immediately makes clear what you intend. (And notice how every three hours between 10AM And 6PM is only ten AM, one and four PM.)