If you can't ID the fruit in a FRESH sour, then you aren't using enough. How many lbs/gallon are you using? Typically, you should use 2 lbs/gallon for a good fruit flavor, and never less than 1 lb/gallon. All sours will lose the actual fruit flavor after they age, but when they're fresh (think fresh Kriek Marriage Parfait or the like), you should really be able to ID the flavor. I typically rack after ~8-10 months onto fruit and let it sit until it tastes good...there is absolutely no definite time period...it depends on temperature, acidity, alcohol %, bacteria count/type and tons of other things. After racking onto fruit, I typically start tasting after ~5 months and bottle/keg when its ready.