One of the features of the find familiar spell is to deliver spells with a range of "touch" cast by the wizard:
Finally, when you cast a spell with a range of touch, your familiar
can deliver the spell as if it had cast the spell. Your familiar must
be within 100 feet of you, and it must use its reaction to deliver the
spell when you cast it. If the spell requires an attack roll, you use
your attack modifier for the roll.
The use of the familiar's reaction to deliver the spell seems to be geared toward touch spells that can be cast on a single turn, such as shocking grasp.
However, suppose I want to cast identify on an object out of my reach by having my owl familiar fly up and land on it, and then cast the spell with the familiar touching the object. Could I have the familiar spend 1 minute sitting on the object while I cast the identify spell?
If so, does the familiar simply spend 10 rounds using its reaction each round to continue delivering the spell? Or does the requirement for delivering the spell using the familiar's reaction limit this feature to only spells that can be cast during a single turn?
Best Answer
Yes, RAW, you can cast longer spells through your familiar.
According to the section on Longer Casting Time:
The Find Familiar spell states(emphasis mine):
This means that, as long as you are casting the spell through the familiar, the spell acts as if the familiar is casting it, in terms of how it is delivered. So, as long as you cast the spell and your familiar uses a reaction every turn, your familiar is touching the target and you maintain concentration, you should be able to cast spells with longer cast times through your familiar.
Any interpretation which states that you must be the one touching the object, not only prevents you from casting spells that take more than one turn, it prevents you from casting touch spells trough your familiar entirely. For example, Shocking Grasp states (emphasis mine):
So, casting it at a distance wouldn't work under this interpretation.