No - six weeks after the flowers are finished, you can pull or cut off the top growth.

Just rake your fingers through them so that they are looking slightly tidier and lying flat.Tying them will reduce the amount of light the leaves are recieving. They need light to photosynthesise and make their food. That food will then return down into the bulb as the leaves die, so that there will be a store of food in the bulb enough to flower next year. A liquid feed periodically after they have flowered will help the bulbs build up also.

Ive always been told and bought up by saying NO donot tie them up and even im sure in saying that even the tv gardening presenters are against this.
My neighbour before he died was all for it, but the daffs would still grow the following year and bloom when not tie-ing them up.
But there again different people have different views of doing this

In my experience they can be tied when the leaves are mostly yellow, but that's just a couple weeks before you can cut them off, anyway.