Best time to buy

Hello. I'm a FTB and currently renting. My husband and I are desperately attempting to save to get out of this renting nightmare and are hoping to get a mortgage this year. Our tenancy ends at the end of September.

I've seen the best time to look for houses is spring time when homes start to come on the market. However I've been looking at how long it takes to exchange and some have experienced a very quick process (normally when there's no onward chain) and others have had the process drag on for ages.

I don't want to be put in a position where we're left with nowhere to live if we give notice and then suddenly the seller pulls out

What would you advise? When would be he best time to buy. We're going to continue saving after we get a mortgage in principle, in the event we need to pay for both a mortgage and rent for a month or 2.