Less than six months, from first purchase to a completed device. This is a personal record!
In May 2015 I bought some Burroughs B5092 Nixie tubes. Since I couldn't build something meaningful out of three working tubes I opted for a dual-digit clock, and a third B5092 stays as spare.
Inside a decoupage light-wooden box I fit the two sockets, a perfboard with K155DI BCD decoder/drivers, an Arduino clone board with DS1307 RTC and a lumos.sk high voltage PSU.
This clock has been built with components of the Cold War era, from both sides of the wall, mixed with modern microcontrollers and switching power supply.
The firmware shows HH, MM and SS. Every hour all symbols are looped once in a basic cathode de-poisoning routine. I have not implemented any other fancy feature like fading, DST auto.adjust, night mode and so on: it is a simple addictive clock.
Yes, I caught people staring at the box for few cycles before asking what are those numbers.
Edit March 2016: the schematic diagram is now available.