CRON for the following timing

Hi,

I want to trigger a bot at 8:30 in the morning and have it run every fifteen minutes.

I have tried this following but it does not work.

30/15 8 * * *

Can anyone help me with the expression as whatever I seem to try gives me a

Invalid cron expression syntax (#1600)

@SRoy

What is the closing time? Start time is 8.00 in morning, but what is the end time?

Thanks

sorry the closing time can be 8:00 pm in the evening thank you for working on this.

Another scenarios is , can it be set to run every 15 minutes starting at 8:00 am till forever ?

@SRoy

Try below expression

0 0/15 8-20 ? * * *

Mark as solution if this helps

Thanks