Our DM cast web on us, and we were all asked to make saving throws immediately. He said, "Otherwise you’re all like Schroedinger's Cats waiting to see if you’ve been caught or not" (which affects attacks on us).
However, those that weren't restrained had to make saving throws again at the start of our turns (no problem with that since the rules clearly specify).
It is difficult to argue with our DM that we shouldn’t make saving throws when it is first cast.
When should we make our first saving throw?
Best Answer
At the start of your turn
According to the official spell description for web:
(Emphasis Mine)
The spell, when cast, fills the entire area at once (unless described otherwise by the DM). That means each of you has to make a Dexterity Saving Throw on the beginning of your respective first turns after the spell is cast, becoming restrained if the save is failed.
Just a quick note: Usually the DM will ask you to roll the Saving Throw when the spell is cast to save some time, instead of asking each individual on their turn.