Hmm, maybe L suspects you're Kira and is testing to see if you call on your own. But you must weigh out the options. If you call L now, he'll think you are being too hasty and are paranoid, which would definitely mean you are Kira, because you're trying to hard to convince him that you are concerned. If you wait too long, L will think you are complacent in helping out with the case and that if you aren't fully involved, then your initial involvement was just to placate him, so that he wouldn't think you were Kira...so taking too long would tip you off as Kira. On other hand, if you wait just the right amount of time, L will predict that someone as cunning as Kira would know the perfect time to call back.