We’ve done 8-hour dosing since our son was 1 month old (he 2 1/2 now) and he hasn’t had sleep issues.  We use a 1ml oral syringe to dissolve the meds, put them into his mouth with that, and then follow up with a few syringe-fuls of water to make sure that all the meds go down and don’t sit on his teeth.

Good luck,