The bottom line is that what you have left for Methadone is just a trifling mindfuck. If I were you, I would be investing this energy into coming up with a realistic plan before you end up going into withdrawal.
At any rate, I would definitely wait until you're feeling fairly sick as others have stated. I would ultimately take the remaining dose strategically when you need to sleep. I'll echo what others have said; you have been taking large doses for the past couple days so you should be straight for 72 hours.
Do you have dough? Are you able to acquire so-called comfort medications? And weed?
Remember what happened to Pinnochio when he gave into temptation? One thing led to another and he was smoking butts with donkey ears inside a whale's tummy.
Dont take that dose now. Please get back to me regarding what you have available to you. Are you in a city? Desperate times call for desperate measures and as I've already covered, you're on a timeframe. Once you get sick, things will become a lot more difficult.
If you're willing to "put yourself out there", it's my experience that bums exchange Gabapentin (Neurontin) like how the Lakota traded tobacco as currency. Gabapentinoids are helpful to a lot of people who are withdrawing.
Quetiapine (Seroquel) will do "something" but, if you're really sick, you can end up in this zombified state in which your totally sedated but still rattling like fuck on the inside. The only way I feel it will be truly helpful is if combined with other drugs.
Please tell me everything significant about your experience dude. You will live and we will make sure you get to where you need to be. My mailbox is always open
P.S. comparing is usually not helpful, but there are guys sitting in solitary confinement coming off 150mg of Methadone with no hope of relief. The 8th circle of Dante's hell!