1-2 weeks would give time for roots to colonize new volume before flower.. this would definitely have a positive impact.
With 1-2 weeks plus 3+ weeks of growth after flower (if accurately guessing flower phase initiation), that plant has a ton of growth potential left. If the roots are cramped, that will stop/slow growth. If growth has already slowed or stalled out, this will definitely help.
I've potted up ~400 times and yet to see a negative effect. Not once have i seen a plant stall out or otherwise slow down. The effect is always positive. No worries. The timing her is perfect, if you really do have 1-2 weeks before flower phase starts. (if it is an apples to apples comparison to changing to 12/12 indoors as far as timing) Also, it's part of my SOP to put up 7-10 days before i change to 12/12 (flower). Roots fill in and make proper use of the added volume.
I think that believe is tied to transplanting plants that are in the earth. That involves cutting off 95% of their root system and is incredibly stressful to the plant. Potting up is not the same. This process should incur no damage and should not disturb the rootball when done properly.