Ambiguous language

I have my Autism assessment soon. The conformation email has this wording:

"Please click the button below anytime up to 10 minutes before your appointment is due to start. You will be admitted once your doctor arrives."

I initially got confused trying to work this out and thought it meant I have to click  the attend button no later than 10 minutes before the appointment. So at least 10 minutes early.

On reflection though I think it's more likely that they want me to click to join the appointment within 10 minutes of the appointment start time but no earlier. 

Their language seems annoyingly ambiguous, particularly when it's being sent to people who are quite likely to be Autistic!

Maybe it's part of the assessment? (sarcastic joke)

One of my kids said to click on it exactly 10 minutes before.