There isn’t a standard viva format.

There are reasonable expectations, but no guarantees.

Probable durations, but very long and very short outliers.

A range of possible first questions, but no certainty for the exact start of your viva.

There’s no standard format, but there are standards: standards for your examiners, standards for the process, standards for what a good thesis might be like.

Be confident that you meet the standard for a good, talented researcher.