^ no your not going to be able to harvest an outdoor crop in 4 months, unless your photoperiod, and weather allows it. however long it takes to grow outdoors depends on climate, light and strain of the marijuana. There is no set time.
It's the same time required for outdoors or indoor, say 8 weeks to flower but you have no control over when it starts outdoors. Most strains outdoors will finish in October but they could be started anytime over the summer.
Seeds to weed takes me about 9 months in the uk growing outdoors
I start the seeds off in march,harvest in october and bye the time it has dried it is usually about december before I get the chance to test it.
It usually takes about 3-7 days for the seeds to sprout