No, you're failing to understand the definition of half life. 100mgs is 100mgs
It takes about a week for bloods to peak on var, so as long as you're dosing about every 8 hours the week leading up to peak, you should be fine.
After that, you can just split the dose into an a.m. and p.m. dose.
Taking an oral preworkout has no benefit, as it doesn't give you an immediate boost. If you think you feel more pumped, it's placebo.