I'd make the pre-workout dose your last dose of the day.
You can stick with 4 caps if you'd like to stretch that bottle as far as it'll go. It would be beneficial to include an AM dose on an empty stomach as well.
Are you using any other supplements as well? The reason I ask is that the (4-6 caps) goes GREAT with 4-6 Cissus and some creatine. If nothing else, add the creatine in. CEE or Mono.
Also, what time do you go to bed?