Flowering starts when you flip the lights. The 55 days you are talking about is most likely an average. Depending on all kinds of differences in growing styles your's might come in sooner or later. The only real way to tell is by watching the trichs which will take a strong magnifier to see. The lil "balls" that you will see resemble a golf ball sitting on a tee. What you want is the color of these lil things to be mostly cloudy. Clear is to early and amber is beyond. Flush is done the final week of flower before harvest.