The tubes are pretty much rated for anywhere between 5,000 hours and 200,000 hours. They should last for a pretty long time (5 years with digit-cycling and night dimming is very reasonable) but because they are new-old stock technology made in Soviet Russia, there isn't a certified life time for them.
In the case that you receive an unlucky tube that goes out in the first month, we'll ship you out a replacement with a tool that will make it very easy to replace.
With that said, these tubes are really durable pieces of technology. They were designed to go into wartime equipment and endure very harsh conditions.We test each tube that we use, and you should expect them to at least 5 years!
Here's a video with more information on the tubes of the Nixie Ramos: http://www.youtube.com/watch?v=EPhnmCHtd8Q