I'd base my decision on how well the cat is settling in, not on a finite time period. Some cats setlle after a couple of weeks, others take longer. None would be allowed outside until they are chipped. At present I have two newbies, Smidgen and Esther. Smidgen is around 16 weeks (b. 8 May) and Esther is a rescue cat of indeterminate age, but an adult. She is fairly timid and does not like being picked up. She startles when new sudden events occur and can be reluctant to be approached. She alone will not be allowed out until she is comfortable with me walking up to her and picking her up and allowing me to hold her long enough to get her inside. She will also not be allowed out until she responds to her name by coming to me.
Smidgen is rather more confident and so, in normal circumstances would probably be venturing outside, supervised, already except a) he is not chipped and has not finished his vaccination course and b) I have an urban fox over the back fence and he is not yet big enough to face it down. I have had them since the end of July, to give you an idea of timescales.
Hope this helps you make your decision. Some cats never go outside and I have had several who fall into this category. As long as you can provide them with lots of physical activity and mental stimulation, they are fine with this.
Best of luck and welcome to Purrs.