Online English lessons

I am referring to online English lessons
There are slots for lessons. One slot is for one lesson.
I am a student and I am supposed to book a slot online.

The below is a question from my teacher.
He wants to open a slot for me.
What time are you free to book tomorrow’s lesson so I can open slots.

I do not understand the part, free.
Which sentence does this imply ?

1) What time are you convenient for your lesson so I can open slots.?
2) What time are you ready to make your reservation so I can open slots ?