Good evening. I started the game playing as the Vaulters but Argosy needs a lot of turns for planet colonization. is there anything that decreases the number of turns for that?

There is not, though playing in faster game modes does speed it up. The entire point of their colonization method is that they can skip the colony stage and get some sweet bonuses for a while by spending some resources (which decreases over time, until eventually reaching 0). In case you are new to the game, I'd recommend only colonizing system that are extremely good, and sucking up minor factions whenever possible as they let you skip using the Argosy. The Vaulters can afford to wait a while to colonize, and since they can use portals, they don't even need to colonize nearby their capital.

CaptainCobbs wrote:

 is that they can skip the colony stage and get some sweet bonuses for a while by spending some resources (which decreases over time, until eventually reaching 0). 

How can I do this?

Oops, I meant outpost stage. It instantly becomes a colony. You do this simply by colonizing a planet, immediately after that you can use it.

Thanks Cobbs.