I have a suggestion how to make it better.
Let say the person moves in to his/her the tribe area. The counter(A) starts countdown from 30 mins. When the counter reaches 0, the players save zone removed. Now he/she can be attacked. Once the person moves out of tribe area, the other counter(B) starts countdown from 15 min.
The counter(B) is to keep track time outside the tribe area. Once the counter(B) goes 0, it will add 30 mins for the tribe area counter(A). Now the tribe area counter(A) is above 0, this means when the person goes back to tribe area, the area will be safe zone again.
That way players wont spend all the time on tribe area, and if they do, they are open for PVP.

EDIT: One more thought.
Let say, the evil player came to someone's tribe area. and that evil player spends about 3 min on that tribe area without leaving the tribe area. Now for that evil player the tribe area opens up for PVP. Its your fault that you didnt killed him or asked him to leave within that time frame.
Once the evil player leaves the tribe area, the counter is reset in 3 min.

Everyone is happy now


Player A outside the someone's tribe area. Counter=3min
Player A moves into the someones tribe area. Counter=3min and decreasing
If Player A moves out tribe area. Counter=3min again
Player A moves back to tribe area. Counter=3min and decreasing
Player A stays on tribe area. counter decreasing, reached 0 min
Player A now can attack that tribe members.
Player A, scared, runs out of tribe area. Counter(b) counts upto 3mins.
When counter(b) reached 3mins , player A counter(a) resets back to 3min, Player A, no longer can attack members on tribe area, counter(b)=0, resets;

Anyone have any comments???