When is the best time of the year to remove old fencing and install new?

I need to replace my fencing but I do pity the poor gardener who will be working in this weather. When is the best time to do this. Winter the ground is hard - weeds are tough to pull. Summer, everything is growing including the weeds. Which is best?|||You can do it at any time. The fencer will be used to all kinds of weather. If the ground is frozen hard then obviously the new holes cannot be dug; but speak to the fencer, he will advise you.|||You can do it at any time. The fencer will be used to all kinds of weather. If the ground is frozen hard then obviously the new holes cannot be dug; but speak to the fencer, he will advise you.|||Late Spring|||fall