Yes, Bambineos (actually, correctly "Bambinex") and other bamboo nappies do take a lot longer to dry than other nappies. You may see some people advertising bamboo nappies as faster drying than cotton. In fact, if you have the same size (weight, knit) piece of bamboo and cotton, and add the same amount of water to each, the bamboo will dry faster. However they're so absorbant that they absorb more water in the machine, so have more to evaporate!
You will find, though, that they stay nice and soft (as long as they're not dried on top of a radiator) unlike cotton which will go horrid and scratchy when not tumbled. They are also extremely absorbant, anti bacterial and anti fungal, and of course the most eco friendly nappy.
If you're struggling with drying I would suggest a combination of bamboo nappies and teddy nappies (Bambinex Teddys have just come out today, and the Tots Bots Fluffle is also made from a teddy fleece. There may be others but I actually haven't come across any other 2 part teddys - anyone want to enlighten me?).
I prefer the Bambinex teddy because it's neater and not as bulky as the Fluffle, but they're both superb nappies.
The point of teddy fabric is that it dries REALLY fast - say 2-3 hours on a warm day - and never, ever goes hard or anything other than snuggly, like a teddy bear. Gorgeous. Only disadvantages are that it's not a natural fabric and it's bulkier than other fabrics. It's more absorbant than cotton so I wouldn't really bother with cotton, myself. I would just go with a combo of bamboo and teddy.
Just my thoughts!
Emma