
Haemon, did you brew a Belgian Christmas ale yesterday, with an OG of 1.068, and no yeast available other than a slant of the yeast you want to use?
My understanding of slanting yeast, means you need at least a full weak of scaling up starters to get to a good 1-2 litre pitching volume.
If it were me, at this point I would be looking for a whole vial of liquid yeast (or 2 of I had it), or at least 2 packets of dry yeast, and just get to pitching. (e.g. I'd rather sub 2 packets of Safeale US-05 for a fancy WLP072 or a slant of a cool yeast, which has not progressively been brought up to proper cell counts.) You'll get a good beer out of a different yeast strain, at resonably close pitching levels. That may not be true of serious underpitching your slant, or delaying pitching a few days.
Side note: I hear that in Australia, some homebrewers do package their wort and keep it for several days or weeks before pitching. However, they fill plastic cubes to the brim, so that there is no airspace, then cap while still very hot. They let it air cool to the next day or so, then pitch and get on with it.
Bottom line, try to find a good yeast quantity, even if it is a different strain than you enviosioned, and get to pitching sooner, rather than later.

Good Luck
--LexusChris