valentt:

It seams that sometime in the past support for hardware rtc devices was removed from kernel:
https://patches.linaro.org/patch/1235/

But this is quite important feature to a lot of people who are building iot devices or just want their routers to have correct time even when they are offline and some time without power.

Manually enabling rtc support and using rtc device like sparkfun ds1307 hardware clock works as expected.

Here are steps I used to get rtc support enabled in latest OpenWrt git code:
http://kernelreloaded.com/adding-rtc-to-openwrt-devices-part-2/

Please consider enabling rtc support again kernel and make rtc kernel modules available as packages.