Open your glove compartment, and take out the Owner's Manual.
It will contain the official Toyota Maintenance Schedule.
You will note that all maintenance procedures have both an odometer mileage value and an elapsed time value, with the proviso, "whichever comes first". For instance, on more recently-manufactured Toyotas, I believe that the interval is expressed as 5,000 miles or 6 months, whichever comes first.
In your maintenance schedule, there could be different intervals listed.
So, in answer to your question, "Which is it, miles or date?", the answer is:
In your case, it would be done on the basis of date (elapsed time).
In the case of someone who does a lot of driving, it would be done on the basis of odometer miles.