Not to challenge what has been said, and for most brews all would be true, but not really the same for a wheat. Wheat beer are best when young, and after a few months they are already degrading when most beers are still not quite to peak.
Wheats don't even really need secondaries, since the purpose of a secondary is to clear the beer and drop out all the yeast, and that is not what you want to do. I typically go 2 weeks in primary, then right to the bottle.
The yeast in wheat beers acts a little differently than a regular ale strain, working faster (hence the need for blow-offs on wheats a lot) than a regular ale strain, and also dying off faster. As Jamil Z put it, they live hard and die fast. The yeast will begin to die off much faster than regular yeasts sice they have worn themselves out, and that will cause off flavors. Commercial breweries get away with it by filtering out the wheat yeast, and adding back a more stable lager yeast to bottle condition with.
That all being said, 4 weeks will be no problem, but you could probably bottle now. If it insn't cloudy like a wheat normally would be, you can call it a Krystalwiesen. It will still take a few months for the off-flavors to begin to show up, but drink these young for the best impression.
