Model Netgear WNDR4700/WNDR4720 Series
Firmware Version LEDE Reboot 17.01.4 r3560-79f57e422d / LuCI lede-17.01 branch (git-17.290.79498-d3f0685)
Kernel Version 4.4.92
Local Time Fri Feb 16 14:28:30 2018
Uptime 18d 2h 20m 42s
A good indicator would be the kernel compilation date, which gets printed if you call # uname -a, e.g.:
# uname -a
Linux lede 4.4.115 #0 SMP Wed Feb 14 22:57:17 2018 mips GNU/Linux
Here, you can see this kernel (and the matching firmware) was compiled on February 14th (self-compiled from the 17.01 git, in case you wonder about the higher number).
However, you shouldn't focus too much on the date. What's important is the git hash (ie 79f57e422d), which allows you to retrieve the same 'state' from the git tree in case you'd like to build yourself. That's more important than the actual release date. The release number itself is linear, so - there's no 17.01.5, which means you're on the latest stable release.