/bin/date --help
BusyBox v1.19.4 (2014-09-03 19:18:17 CEST) multi-call binary.

BusyBox's Date does not support "%N".

opkg update
opkg list |grep date
coreutils-date - 8.16-1 - Full version of standard GNU date utility. Normally, you would not use this package, since the functionality in BusyBox is more than sufficient.

Not true this case.

opkg update
opkg install coreutils-date
/usr/bin/date "+%d/%m/%Y%l:%M:%S::%N"
16/11/2014 2:08:14::883694217