Mix it up two or three days ahead of time if kept at room temperature and you should be ok. Refrigerated...mix it today and it should be fine till next week (take it out of the fridge the day before you get your bees so it can warm up).
I don't know how many packages you are getting, but as a newbee myself I've found that I need to make up the occasional quart or two "on the fly". I feed with quart mason jars. What I found is that I can put 3 cups of sugar in the jar, then fill the jar up about 90% full with HOT tap water and stir it up good. Next, fill it on up to about 1/4" from the top and put a solid lid on. Shake this up good and you end up with a very good 1:1 mix. I've even got it to the point where I know where to fill the jars with sugar and don't have to use a measuring cup...I fill with sugar to the bottom of the "L" in Atlas...I'm using some old mason jars
Vitamin-C tablets (ascorbic acid) is know to help the syrup stay good and also supposedly lowers the pH to a pH more amiable to the bee's gut. Do a search here on beemaster is you're interested...
But anyhow, 3 cups sugar in a quart jar and finish it off with HOT tap water and you're good to go for a 1:1 mix.