I usually toss em in after fermentation is about done, but how much, and how long?
Pellets are much easier to work with imo. Especially in carboys. Its hard stuffing leaf hops in. They also drop out nicely without need for a hopsack. I toss mine straight into primary for 5-7 days. 3 oz per 5 gallons Id say is the max before things get a little grassy/vegetal.
I like pellet hops myself. They settle out pretty nicely 
Just read the thread in dry hopping below…
Answered allot of my questions!
It also depends on the recipe. The Pliny recipe has dry hops in it from day 5 to day 14. I toss them in and give the carboy a gentle swirl every other day just to get them back in suspension.
I remember reading something from a major brewery (maybe NB?) about how extraction of volatile compounds peaks within 24 hours when dry-hopping. Not sure how applicable that is with homebrew-sized batches, but it makes me wonder if I’ve been dry-hopping for too many days.
I’m usually never on a charge of dryhops for more than a week.
I’ll dry hop at the end of primary and then in the keg. More hops and less contact time isn’t exactly efficient, but it provides a more intense hop presence without grassy, dirty, vegetal off flavors (that I can detect, anyway).
I’ve been experimenting with sulfites to minimize oxidation, especially when dry-hopping. I haven’t really decided how useful it is for beer yet. There’s nothing I hate more than cardboard hops.
I dry hop with whole hops. I brew my Pale Ales, IPA’s in a bucket and add the dry hops in mesh bags weighted with the glass aquarium “rocks.” When I use pellet hops, the float on top and NEVER settle to the bottom. I’d love to know why pellets settle out for everyone else.
Probably 1/3 of my hop pellets sink, the other 2/3 float on top, if left alone.
Now, I don’t know much about quantum physics but… ( 
that’s for you nateo)
I think it’s got something to do with how much air is trapped betwixt the bracts of the whole cones vs the pellets.
We’re all climbing our own “Mount Stupids.” I’m still at the bottom of mine re:why some of my hops float and some don’t. I know it’s something to do with buoyancy, but beyond knowing what “buoyancy” means I’ve got nothing. I think I can rule out cosmic rays and ether as possible contributing factors, but beyond that I’m clueless.
I dry hopped an ESB for 12days with a good outcome, actually not as floral/aroma as i expected, i also dry an IPA for 16days (simply no time to bottle on both occasions) the IPA turned out well maybe a tad to dank/vegetal but still very drinkable. both times with pellets very easy.
What kind of hops did you use? I’ve let some Willammette go for a long time and wasn’t really happy with it, while I let one of the C’s (Chinook?) go for a long time and it turned out pretty well. So maybe variety has an effect?
for the IPA the hops were Amarillo, Citra, Chinook, and Centennial the aroma is great, but heavy grapefruit and dank smell/taste
for the ESB the hops were fuggles and galena
For a 5 gallon batch I use 2 oz in an APA/XPA, and 3-4 oz in an IPA. I noticed a huge difference when I went from 1 to 2 ounces, but I haven’t done enough 3-4oz batches to decide whether that gives significantly more hop aroma than 2 oz.
I’ll use either whole cone or pellet hops, depending on what I have on hand. I haven’t noticed a difference between the two, so I prefer pellets when I can since they soak up less beer.
I don’t bag my hops, I just dump them in the fermenter (I prefer buckets to carboys for dry hopped beers for this reason). I line my bottling bucket with a paint strainer bag when I rack over to catch any hop bits that may make it through the autosiphon. I have “punched down” the floating hops when using a large amount of whole cones for dry-hopping, but now I just give them a couple of extra days. They seem to take a while to hydrate completely, so I just give them some extra time.
I dry hop for 10-14 days at 68F. I have yet to notice any vegetal character in my dry-hopped beers. I can’t say for sure that the warmer temperature makes the difference, but this has been working for me, so I’m sticking by it.
What hasn’t seem to have been mentioned is that there are less vegetative matter in pallets as opposed to whole so you should get less vegetative flavors with pellets. Also, whole hops soak up a lot more beer so you will lose more with whole hops. I have never had a problem with pellets dropping out. I use conicals now almost exclusively and I dump my hops in and don’t have any issues with carry over. OTOH I do BBT every beer.
I use whichever smell better when I’m ready to dry hop. 1-3 oz. for a week or so, then usually another 1-3 oz. in the keg.
Denny, does the sure screen work well with pellet hops in the keg??
So far, so good! Although I usually bag them.