When To Change Age Specific Food?

I can't seem to find any information on when to change a rabbits diet from Junior to adult, and from adult to mature?
The bunny in question will be a mini lop (on waiting list for one)
Do i change her food in the age stages or should I leave her on the Junior/Dwarf? I was thinking about switching to the Supa Rabbit Lite from the junior for its slightly higher fibre content. Anyone have any thoughts on this?

I think its when they are 12 months old you need to wean them off the junior food onto adult food. On Science Selective mature food bag it says its for rabbits aged 4 to 6 years plus.

Thank you x