It is all guess work, the +/-s does not really mean anything, the only time a tribe can work even close together is if they are all from the same country as some people are reluctant to agree on a set time format ie GMT etc as there is no server clock to work to, and, if i set a noble train going and tell my tribe what time it arrives, gaurenteed i can look 20min later and the train arrives 10 seconds after i told my tribe mates, and that ten seconds gives a big gap for a target to fill the village with troops avoiding the clearing troops completely.