Given the combination of global warming and the recent renewed interest in Sloe Gin in the last few years, you probably won't have any left to pick by then.
I think they are a bit early this year. Just had a short break with Mrs V in Somerset and on a walk noticed a burgeoning crop of local Sloes,however, I have branched out in to Raspberry Gin and Blackberry Brandy.Still not attempted Rhubarb Vodka though.