9 or nine

Depends on the stylebook you subscribe to. The Associated Press Stylebook suggests spelling out single digit numbers (one through nine) and using figures for 10 and above. However, The Chicago Manual of Style recommends spelling out whole numbers one through one hundred. I use the AP method myself.

So IMO, the answer is "nine."

The McTag Stylebook suggests Tico is right. It is better to use the written form of the number for a good prose style.

It depends a lot upon the context, though.

Please come by 9 tomorrow morning
Please come before nine tomorrow morning
Please arrive before 09:00 tomorrow
Please come before nine o'clock tomorrow morning

All are acceptable

Thanks fior your guidance.