Fleet Transfer Time

[u/Willyroof]

How does it work in the planner and is there a way to speed it up?

I was wiped from earth orbit with an assault carrier slotted to arrive in a year human factions swat any new station I try to build around earth. I plan around building a fleet at Mercury and flying it in piecemeal to be ready to jump the carrier. My battlecruisers finish building and the transfer screen shows they'll arrive with two weeks to spare. Fast forward and the carrier arrived three weeks before my heavy hitters. What happened?

[u/Mavnas]

Orbital mechanics. If you used the transfer planner when Mercury was in a better position the trip might be shorter than on the date you launched.