It's just a guess. If it looks like as much fruit as leaves then I thin. If not you may be OK. But I try to thin the blossoms. That's much better IMO. So if the bloom looks really thick strip some off. Or as an alternative thin out much of the smaller wood or trim some fruit buds off the ends of smaller shoots.

Another thing I've done is once it sets as much fruit as I think it can handle, thin off all later blossoms.

The only thinning I know about with blueberries is the thinning/pruning of shoots. I have not read about thinning blossoms or fruit directly. The fruit clusters, at least on southern highbush, seem to ripen in stages. For that reason, thinning within the clusters doesn't make much sense if you've thinned the shoots correctly.

Here is a link that might be useful: CARE OF SOUTHERN HIGHBUSH BLUEBERRIES

Thanks, I think I should be OK then. I will not take any off and see what the end results are.