A local veg grower told me to reckon 12 weeks from planting. You could scrape a little soil away and see how big the first ones you see are but i would leave them a few more weeks if they were mine. Unless you have been watering them a bit they will only be small anyway.

Normally once flowers appear, but it is early days unless you are in a very southerly aspect, like Cornwall or Channel Islands

He's in Derbyshire Grandad, so agree best to leave them a bit longer. I've always reckoned July, about the same time gooseberries are ripe...