It also depends what temperature you have it at. I had one a +80 this summer and it formed in 3-4weeks and fell at 8 weeks. Though I was not too happy with the result. The batch was soured well, but was not vary complex. I think with these types of beers it much better to keep it cool and age it for at least a year. but like others say, don't expect to see the pellicile layer for a while.