Should I suggest a time when professor want to schedule an interview, or just say I always available ?
In this situation, pick a preferred time within the professor's constraints, and suggest it.  To be safe, propose a back-up (perhaps the following day) in case anything goes wrong.

Additional tip: Suppose the professor said he's available after 10 am.  Then to give him a little margin for error, I advise choosing a slightly later time, such as 10:30 am.