Fleet returns take a long time

[elopez]

If you send a fleet on a mission somewhere, and then ask it to return before it arrives, the return time is erroneously calculated.

Steps to reproduce:

1. Send fleet to an allied planet with mission "maintain position". Let's say it takes 2 hours to get there and 2 hours to return to our planet
2. Wait 10 minutes
3. Press "return" on the fleet base

Expected behaviour:

The fleet gets back in 10 minutes, as it is only 10 minutes away from our planet.

What happens:

You will see the fleet will get back to the planet in 2 hours.