I've had angels go from free swimmers to large 2" (body sans fins)in 8 months. within 1 year these angels are as big as their parents.
(ever seen wigglers? it's amazing how large they get and how fast.)
if you get quarter size angel give them room and food..they will get pretty big in 3 months.
I picked up quarter sized wild Scalare (Peru) last July/Aug..they are already as big as my adult domestic angels and still growing. they are all either paired up or single in large tanks(29-75 gal)
I would say you have 8 maybe 12 weeks.