how long do you lager a maibock? or other similarly high OG lager?

I’ve seen anywhere from 3 to 18 weeks, which is quite the range.  How long do you lager your maibocks or high-OG beers?

3 or 4 weeks should be plenty in my experience. Maybe even less in some cases. However The only right answer is “long enough until it tastes good to YOU”.

^^^^^ This.
I lager until they are clear. I know a lot of people, including Gordon Strong, say it needs to be lagered 1 week for every degree plato, but I have never known that to be true. A good beer is good right away. The lagering helps to drop yeast, clear the beer (drops tannins) and meld the flavors.

Remember that extended lagering increases the likelihood of oxidation, unless you have a very good control over oxygen ingress.

+1 - 2-3 weeks probably is actually plenty. The flavors may round out a little after some aging but even high gravity beers are often best when they are relatively fresh. The difference being that they may age better (or they may not).

If you use gelatin or other post fermentation finings like biofine clear that certainly speeds up the clarifying aspect of lagering.

I agree that even somewhat bigger lager beers are still better when relatively fresh - I don’t see significant improvement after a month, but being a bigger beer seems to allow for less loss of flavor with modest aging.  All said, about 3 weeks is when I tend to notice a lager beer hitting its stride and with a Maibock, it should hold up well for 2-3 months (longer if closed transfers are used to minimize O2).  With small ABV lagers (which I typically brew) they are fully ready in 2 weeks (done fermenting in 6-7 days on average).