It's not a bug.
The time specified in the mail is the time of your server. The time specified in the summon window is your time zone.
For example, to enter the game I use an oasis account and my time is specified in the profile, that is GMT+6. My server time is GMT+8. The leader indicates the capture time at 20:00 by server time. But the summon window shows my time 18:00.