Bfb, 6x, chicken manure pellets are all concentrated food and best used where plants are growing. So if you are now planting, yes spread them, otherwise the weeds will benefit, and they don’t have a mulching effect, unlike compost.
Leek rust is more common in dry soil so either water, and’or spread a compost mulch, or even a grass or hay or leaf mulch as leeks are not too troubled by slugs.