I just started a bunch of seed outdoors myself. At this point, It's basically like doing 12/12 from seed indoors.
Most hybrids will start flowering in mid to late July outdoors, and will finish in October.
The closer you get to a pure equatorial sativa, the later it'll start to flower and the longer it'll take.
Ultimately, the advantages of starting seed earlier in the season are that your plants will get bigger and thus yield more, and they'll be more likely to reach sexual maturity before flowering is triggered, which allows you to cull any plants with undesirable structure or males if you're not interested in making seed.
Are these going into a guerrilla plot or a back yard?
Keep us posted!