Priming mixture sitting in bottling bucket too long?

So I am planning on bottling tomorrow and am splitting the batch 3 gallons normal: 2 gallons with added blueberry extract (yes real fruit is 'better', but that's not the point of this thread ). I'm was planning on siphoning all 5 gallons into the bottling bucket at once to avoid having to siphon twice and risk more contamination plus save some time (I don't use an autosiphon), then bottling 3 gallons of it, then adding a little extract to the remaining 2 gallons, stirring gently, & finally bottle the remaining 2 gallons. This should only take about 5 additional minutes, but you never know.

Anyways, how long do I have before I start to lose a significant amount of CO2 from the yeast eating away the priming sugar before getting them bottled and capped?

Nah man ur fine... it'll take days to start losing the CO2 from the priming sugar.

But your better off siphoning all 5 at once and mixing it with the priming sugar, that way it will carb uniformly, rather then have to split up ur priming sugar into 2/5th and 3/5th parts.

Your plan sounds fine to me. The yeast will take several days/weeks to finish eating up the additional sugars. An extra 5 or 10 minutes in the bottling bucket will be no problem. The biggest risk would be contamination since there is no co2 blanket in your bottling bucket. You obviously don't want to let it sit in there for hours on end.

It won't take days or weeks to ferment the added priming sugar- but it will certainly take longer than the length of time of adding the extract and bottling.

4 ounces of priming sugar in a 5 gallon batch will ferment pretty quickly, so I wouldn't let it sit for hours or anything like that, but a few extra minutes is fine.

Cool beans, thanks for the quick replies.

Are there any fermentable sugars in the extract?
Might be a little worried about overcarbonation if you're bottling directly after adding the extract.