How long does it usually take to get results back from vets to determine fertile time? New vets have just said they will call me back but said they are sure it takes several days,surely that would be defeating the purpose?

If you use Idexx and get it posted straight away they will ring you the following day. If you are lucky enough to live by an Idexx lab you can drop the sample off first thing in the morning and get result the same afternoon

My vet uses there normal lab ( not Iddex ) Draws blood am, courier to lab before lunchtime and result same day approx 5pm

Idexx will be next day but you must chase yor vets and the reading is the day before