Topsoil for Lawn - best times?

[TomDunreedy]

Hi all,

Thinking of placing topsoil on an old patchy lawn.
When is the best time to do this?

I don't want to kill it if I cover it with topsoil.

Can I do it now? In middle of winter?
Or should I wait till spring?

Thanks,
Tom

[Pheonix]

Spring has sprung, the grass has riz I wonder where the birdies is?