This, alongside autumn, is the best time of year to get grass established, so I'd sow if I were you. Have you prepared the soil? Once you have, sow the seeds, give them a good soak and keep the bastard birds off.
Clearing the last of the weeds/ivy today. Soil seems great, to my uneducated eye. Will be scarifying/loosening with an asphalt rake, sowing, raking, pacing over and setting up the sprinkler.
Am I mad to sow grass seed today to try and take advantage of the forecasted good weather, or should I wait?