How can I find out whether my personal tutor (or another academic) is in today?

The easiest way to find out an academic's availability is to email them directly. When you go to email them you will also be able to see if they currently have an out of office on. Please allow a minimum of 48 hours for a reply. 

Additionally, personal tutors often have office hours, which you can just drop by to. If they have an office, their office hours will typically be posted on their door. Their working hours may also be listed on their email signatures and staff profile on their faculty webpage.