My relative has a 2500 bond for a traffic offense he has been arrested how long will he stay in jail

That''s going to depend on the traffic violation. So there's not enough information here to answer the question.  Some traffic violations are fine only. Some are misdemeanors that carry a maximum of 364 days in the local county jail, and some are serious felonies that can lead to serious prison time.  Unless he posts bail per the current orders, he'll remain in jail until the case is over. If he gets sentenced to jail or prison, he will be earning credit for time served.