if you're doing an A/B, I think sodium carbonate would be a viable option, but never tested myself to know for sure.. KOH would also work if you can find it, or just keep looking for NaOH
As for leaving the acid cook, in terms of stability, yeah dont worry at all about dmt... I know that if one leaves for days/weeks/months some acid cook done with vinegar, what can happen is fermentation, so there will be some amount of alcohol which would screw up the extraction later on as the mixed alcohol-water would keep some spice trapped .. But then all one has to do is cook it again for a while before adding the base, to evaporate all the alcohol. (I dont know if this fermentation happens with citric acid, maybe not, but even if it did no problem as I mentioned)
so yeah, dont worry