Thanks for all the replies, that's really helpful. She normally fills her nappy right after tea but that could change so spares make sense. I need to think about 4 or 5 as a minimum then. I'm quite lucky in that we have a huge airing cupboard so I use that to finish off drying damp seams etc so can dry bamboo nappies fully in 48hrs worst case. That said, I haven't yet tried drying any puropose-made night nappies, but a bamboo bbh and bamboo sandys.