If you try to use the calendar without using the mouse there are multiple issues

• it is not possible to navigate from the days to the time
• the time is using an input of select without a corresponding label
• if you are somehow able to select either the hour or minute then if you use the keyboard to change its value the date also changes
• i suspect that time should be a separate table and that would help solve the above
• the absence of any th or scope in the thead makes it impossible to know that 23rd sept is a wednesday
• the same is true for the day wn cell which should be a th with a scope of row so that you know it is the third week
• it is not possible to navigate to any of the three buttons using a keyboard
• it is not possible to navigate to the area to change the month or year using a keyboard