I have been looking to get started in undergraduate research (CS) and finally got a bite on a cold email. This professor said he read my resume and "liked my profile" and asked if I could meet him after X on day Y. I responded asking if a specific time in that time frame worked for him. However, it's been a day and a half and he has yet to respond. (the day is tomorrow)
If he does not respond today, would it be rude to knock on his door during the time frame he specified? Or does the lack of response suggest he has rethought the offer?