Question about take-over Castle

[Quiet_Wildcard]

When I want to take over an castle and i want to prevent a bounce tactic, is it normal when you retreat the first attack time stays the same? Even if you retreat your troops?

For example. I attack at 17:00 o,clock. And the castle is devent for 7 rounds.

I attack first round 17:00 - 17:10
- 17:20
17:30
17:40
17:50
18:00

Now this rounds I didn't put any silver with the troops. But before the last round I retreat al troops!
So there isn't any attack left on the castle.

For the last round I attack also but then 18:05 so... the attack must end @ 18:15. But that didn't!!!!
It ended. 18:10! How that is possible? Is that normal or just a bug? I can't beleave sobody else exactly attacked at the same time! Or did i have to wait always before the attack round stops so I had to attack after 18:10 ???? Please feedback. Thanks