Using beam forming antennas in ad hoc networks have been recently focused on, in order to improve the space reuse. This news context implies to revisit network algorithms because they aren't suited to this new hardware. Moreover, beam forming antenna models used for simulations lacks of realism. At the MAC layer level, packets have to be efficiently scheduled on beams in order to improve the network capacity. We consider two optimize criteria: the antenna throughput and the maximum delay of packets. In this paper, we propose our MAC scheduler, FIFO TBW, based on time windows which takes care of hardware constraints. Then, by studying graph results, we attempt to give a first approach to find good TBW values to optimize the throughput and maximum delay criteria.