The only thing I would say is that leaving a space between the digit and "am" makes it a little confusing. There appear to be various opinions on this forum about how to write times. Personally, I don't use "a.m." but I would not put a space after the digit, so:
9am to 11am.
9am until 11am.
9am till 11am.
By putting "am" immediately after the number, there is no danger of "am" being read as the first person singular present simple of "to be".
Student or Learner