This is just going to train bad flinching habits.
You need to make sure that you are training/ drilling defence at a level where you can apply valid defence.
Build it up slowly over time.
Going on to being hit at constantly isn't going to teach anything about defence.
It may waste your time and give you a bad taste about what sparring is.
The flinch is your very basic reaction to an attack, whatever you do, you don't want to untrain yourself into *not* reacting to an attack.
Once you have confidence in your defence drills, you flinch will become parry, slip or whichever defence works best for you.
Never ever stand there and let someone hit you in the head, even if it's light contact- this is of no benefit to anyone.