Mission briefing for interplanetary missions is useless without specific info about transfer windows and dv requirements.

[The Aziz]

I started the first Duna mission. Keri told me that there needs to be a 45⁰ difference between Duna and Kerbin, and incidentally, in my current position in time, it is.

The delta v planner in VAB (which should also be present in flight but isn't for some reason) tells me I need 1070m/s for the transfer from low orbit. So I set up the maneuver, it intersects Duna orbit, but the planet is nowhere near the craft's position at the time of the intersect.

So what's the deal? Do I still have to use external tools because the game can't give me a straight answer? 

The whole ease of approach for new players gets thrown in the trash when they don't get enough reliable data to get anywhere further than Minmus. And I say this as player with 1500 hours in KSP1.