To add to the excellent posts above me, which if i were you i would strongly consider and basically heed advice you were given, as it's good .Could you answer a couple of questions, because something does not add up for me. How much kratom have you been taking in grams during one day? What is your purpose here, what i mean is your planning to use Tramadol as a painkiller for two weeks only and you've started at 600 mg? Why two weeks only ? Are you using tramadol as an aid to withdraw from kratom? Are you using it as a stop-gap before you get something better for your pain? Or is it for pleasure? Oh and how long time have you stopped kratom before? Have you done tramadol before?
Too much unknowns to give you concrete advice at this point, but in general you are above the seizure threshold. I know what are you getting at with spacing the doses, but imho it is highly anecdotal and highly personalized, ie. i for example due to tolerace etc have used even higher doses and i almost always space my doses in various time-intervals and i haven't had a seizure yet. Did i have at least 4 really close calls .. Yes. My point is that i got lucky, my tolerance to tramadol is/was up to the roof and still i might have a seizure. I remember a couple of posts from this forum of ppl who used for example for 3-4 years, haven't had a seizure, spaced their doses and still had a seizure at some point. It's a risk which if you go above 400 mg will always be there imho. Let's say you take 600 mg, space the dose so you take 100 mgs every hour, so to oversimplify things lets say the half life of tramadol is 6 hours, so by the time you take your last 100 mgs, there's still 550 mgs of tramadol in your system. You will also make the duration of the effects longer that way which for example can fuck up your sleep scheldue (believe me been through it many times). Is it safer than gulping down all the 600 mgs at once, maybe but it isnt a foolproof method to not get a seizure.
As you started doing it anyway, i would broke up that 600 mg ( but first ask yourself do you really need that big of a dose) into 2 x 300 mg. Dose you're first 300 mg after you wake up, dose it anytime between 30 mins - 1 hour ( with 1 hour being the more 'safer' method). Then after your last dose of the morning wait somewhere between 6-8 hours and do same dosing between 30 min - 1h( but be aware that it adds that complexity that may mess up your sleep scheldue) . If you have an access to a benzo, even a small amount with or before your dosing would in a way act as your insurance against the seizure risk.
My only problem is this that for whatever purpose you are using the tramadol, i see that it could easily escalate into dosing more and more and you would end up on a 900 mg a day (as starting on 600 mg is a lot). Add to that a benzo and let's you say you like the effects too much and from there it all snowballs into a bigger problem and it's not worth it. If i am asuming something inappropriate and you truly plan to use it only for two weeks and then stop, then i'm sorry. But if you are using it as an withdrawal aid or a stop gap between getting some other drug or kratom, i would reconsider your dose. You don't need to be high or feel pleasure etc. Try lowering your dose up to a point, where you just feel okay and functional, you could try 400 mgs for starters. If you are using it for pleasure then basically no can predict will you have or won't have a seizure. I feel like the risk will always exist if you go above 400mg. Using a benzo or pregabalin could mitigate that, but of course you could get dependent on them. That's also a risk. Tread carefully. If You space your doses, pay close attention to your body, if you do feel good at a certain point, stop at that and dont redose. Believe me when i tell you that there's risk involved and the reward for that risk ain't that great , so maybe reconsider what you are doing? Wish you well!