Hours or the hours?

the usual classes start at 10, and, now, the teacher would like to change it to 9.00 this one time.

You can simply say, "Yes we can change the time."

We use "the" because this time is one that everyone already knows about. They are "the" normal hours for this class.

Other possibilities:

Yes, we can change the time as you suggest.

Yes, we can change the starting time to 9.

Yes, we can change the hour. (Note that this is quite old-fashioned. I don't think it is used in the 21st century. also, if you used "hours", I would assume a permanent change, not a one-off))

There is a special usage with the plural noun hours.

From Cambridge Dictionary:

hours noun [ plural ] HR, WORKPLACE

• the amount of time during the day or week that you work:
  • reduce/cut/increase sb's hours The company have threatened to cut my hours at work.
  • long/flexible hours People in executive roles often work long hours.

Idiomatic would be 'Yes, we can change your hours'.

'Change the hour' refers to resetting a device incorporating a clock.

If 'change the starting time' etc is intended, this question should be asked on ELL.