Jim,I don't think it matters much in normal circumstances,if all the bait is gone,the barbel(or anything else)will work the way up the swim to a point just above where the feed was introduced,then drop back to their hidey hole and start again and again and again,this is common practice and I've watched it on rivers like the H.Avon,where I would feed every 1.5hrs,fish would still be searching until just before time was up,I don't think much was left apart from an odd grain of hemp,if that,only on rivers like the Trent,Wye,Severn etc do fish put up with continuous casting and feeding,these days when fishing boilies I use small pva bags and cast(if I can)every 40 minutes,my fishing has changed as I used to feed loads of bait,often that just doesn't work today,on the Trent I hear guys I know who fish it saying nobody was catching,it was off,I know others who fish casters and catch plenty,barbel are not as simple as some anglers think,apart from in darkness...