You might be able to get away with the w/c daily,but fry release a growth hormone,so doing w/c daily will encourage them to grow better.
I have 4 guppy fry in the main tank that haven't got eaten has yet,they're a few weeks old now,and they're growing ok,with just a weekly w/c so really its up to you.
I have 300 + fry in my fry tank,and its just habit to do the daily w/c now.
Your fry will soon out grow the trap,so you will need to decide what to do with them.