I would do a time course. The integrin field usually does at least a 2 hour serum starve before adhesion and stimulation with agonist, but you may want to try longer times.
Actually, tried 24hours according to some papers but the effect is not so significant, all cells with FCS free also pjosphprylated. So do you think is necessay to wash the cell with pbs several times before serum starvation?
Depends on phosphorylation event. if you are looking in phosphorylation of MAPkinases, overnight starvation is sufficient (aprox 18h). But washing the cells after removing media with serum is a must. you can wash them just with plain media in which you will starve the cells.