I'd say lash it out there as soon as it's ready.
As a seasoned househunter, here's the way things work from what I see and from speaking to Estate Agents.
The cut off point is the school holidays end of June. So July and August are slow months for selling houses.
The traditionally 'busy' selling season is now until Easter (a lull over the Easter/school holidays), then another selling season from Easter to Summer holidays. Then Sept to Christmas another selling season, but if you don't sell quickly then you are facing into the next Year still unsold.
The way the market is at the moment though - I see a small flurry of new houses (new to the market) being put up for sale in the past couple of weeks.
Normally I'd expect to see a flurry of new houses appearing after Easter as well, and again in September but in the past 2 years this hasn't happened - it is more of a very, very slow trickle at any time of the year.
It is frustrating for the househunter/buyer also, as basically I'm ready and waiting to buy, but the right house is just not coming along.