Benzi bro i'm a bit surprised you're asking this b/c I've answered this question so many times on this board. Not a flame or anything but did you do a search first? If you did not a problem, Well here goes again.
Best place to buy dextrose is supplementsdirect.com, it's 11pounds for $10. Proteinfactory rips you off w/ dextrose pricing.
Only time I would take the dextrose is after a workout, it's when your muscles are depleted and you need that quick flush and insulin spike so all nutrients go into muscle. You can get that insulin spike w/ about 50gdextrose and i use 50g whey. I prefer 70g of dextrose though. Make sure you add no flax or fiber it will dull the spike.
If you're taking Creatine and not to worried about fat, then take the dextrose w/ creatine on other times other than the post workout shake. I personally don't. Mustang18's idea i believe where he took creatine a few times a day, but only time he took it w/ dextrose was w/ the post workout shake. That's a lot of carbs in a dextrose/creatine cocktail.