To increase time between bottles she needs to be taking more at each bottle less than 5oz a bottle is a small amount for a 5 month old, even breastmilk. Breastmilk is digested quicker than formula too, not all breastfed babies make it to 4 hours between milk feeds before they start solids.
Is she draining those bottles? What flow teat do you have her on?
Rather than cluster feeding which is the opposite of what you want you would be better off increasing the size of the feeds she takes.
Laura