We can use have to in all tenses, and also with modal auxiliaries. We conjugate it just like any other main verb. Here are some examples:
subject auxiliary verb main verb have infinitive
past simple I had to work yesterday.
present simple I have to work today.
future simple I will have to work tomorrow.
present continuous She is having to wait.
present perfect We have had to change the time.
modal (may) They may have to do it again.
Now, the question is according to above table, what will be the past perfect form of we have had to change time.
will it be : we had had to change time. If not then what will it be?