Average time for 1st dan is 10-12 years... whew! That is a good illustration of what the different ranks "mean" to the art being practiced. Honestly, knowing the local aikikai folks here in Houston, I'd say the rankings here are either easier.... or they are way better, as they're done in the 6-8 year category (yes I'm just poking).
Tomiki aikido is based on the judo ranking structure, but where the judo curriculum is the gokyu-no-waza (40) techniques, or the shiny new USJA 67 techniques I think it is, I can never remember that one, a strange artifact of this judo rank philosophy is that in Tomiki aikido, we progress really dern quick to shodan. Average is 2, 3 years. Of course, all this means is that you know the basic techniques, know what the principles "are," even if you don't really undertand what they "mean" and "why" they are there.... so you get to this basic level of understanding and then rank progression slows Waaayyyy down. It is not uncommon to fin a tomiki class with 2 or 3 color belts, 6 or 8 black belts and 1 to 3 candy-striper belts indicating rokudan or above. Like I said, an artifact.
A good way to figure out what level of skill someone has, though not really infallible, is "How long you been doing that?"
Someone says, "I've been in judo 15 years," you get the idea. Swap in different martial art name, and you get the same idea. That would be, they probably know their stuff.