if you change after each wee leaking shouldn't be a problem really, unless it is leaking around the legs. if this is happening, the insert may need more washes as it may be repellign the wee, not absorbing it.

for sleeps, they may not be the best nappy. I find most AIO's and pockets are unsuitable for naps if you think they're going to wee as they often only have absorbency in the middle soaker, not near the wings - especially bad for girls as the wee tends to run up the back and soak through near the wings just wide of the soaker pad. this is an annoying trend in nappies - even in some fitteds. I prefer terries for naps for this reason.