Figure it will at least double in size.. potentially more.
because this is an area, must consider l x w dimensions. so... if it is roughly 70% of intended length and width, it should double to "100%" by end of stretch or larger (70%x.70%=.49% of future area covered)
keep those limbs as horizontal as posibble for even growth.. if oyu want some side branching, temporarily restrain apical tip down below that height... tallest nodes take the most resources. Sometimes you gotta force those future vertical branches to pop out a bit... then keep them level after that and all is right as rain.
Even after flip you'll get minimum of 3 weeks of vigorous vegetative growth (leaves + elongation of stems). Most will go longer than that unless it's a fast blooming plant. Some don't fully stup until 6weeks after flip, but will slow down before that point.