I feel like this is going too come down too location and the weather for the particular year Its a rather hard question too answer, there weaned in october so feasibly september?
Technically there stomach Is developed enough between 8-10 weeks for plant digestion but again sensitive little deer would be a miracle if they survive too early winter.
I shot one last year in SW Scotland that I knew was orphaned at the start of doe season It was alone and feeding in 40mph winds at 12pm, the wind was parting the back hairs of Its legs too the bare skin 18lbs including the gambrel so probably 16lbs, I dont think that would of survived considering I shot it mid november.