Didn't think nutes had anything to do with when they will start to flower. As I'm currently growing autos I've been doing a lot of reading up on them and have seen nothing about them staying in veg until you switch to a flowering part. The way you say "I had it in veggie for 54 days until I figured it out and changed it" implies that it's possible to control the veg time? Is that what your saying? On that note, I've not seen anything about controlling veg time and/or inducing flowering by changing nutrients for any type of cannabis plant.
From what I've read and the experience on my grow it will flower when it's ready and if you continued veg nutes it would end up with Nitrogen toxicity. Mine began flowering while I was using veg nutes and i waited a week and then transitioned to bloom nutes.
In answer to OPs question, It's a general rule that they'll go at least 2 weeks past what the seed info says, Could go as far as 4,5 weeks past what it says. Lots of things can play a part.... strain, genetics, growing conditions, stress. If you have an 8 week deadline then I wouldn't make any promises.