How long is a piece of string? No, seriously, it depends very much on what you individual body can tolerate. I personally think a bit of fruit is good for you, from the vitamins, minerals and fibre point of view, so if you can tolerate them, then go for it! If you're having it after a lunch where you've had proteins and fats, this tends to slow down absorption of any sugars, so it's probably the best time to eat one. Because they're small, it's not as if you're having a massive amount of sugar. Do you have a glucose meter? The best way to find out is to test before lunch, and a couple of hours after and see what the result is.