It's been a while since the siege lockout for joining a guild has worked right. Previously, once siege preparation began you had the 2 hour lead up and the 1 hour of siege during which you couldn't invite anyone to a guild. Recently, it changed to the 2 hours of prep period, plus the 1 hour of siege, plus 2 more hours after siege before you could invite anyone.
While I understand this is to prevent people from hopping guilds during siege, I think the system could benefit from the lockouts only being applied to guilds that actually managed to get signed up for that day's siege war. All other guilds should be able to add new members if they wanted without the lockout since the guild hopping protection really wouldn't apply to them. Players should still have a 1 hour period after leaving a guild before they can join another. So even if a player participated in a siege and it ended quickly, if they left that guild to join another they still could not get into a second siege for the same day due to their 1 hour restriction, and the protection in place on guilds participating in siege.