Most folks add it in steps there are many different addition schedules. Some like to add a little every day or every couple days. I usually add half after the lag period as soon as I start to notice active fermentation starting, this can take from several hours to a full day after pitching the yeast. I add the other half at the 1/3 sugar break, this is when 1/3 of the sugars the yeast will consume are eaten. Note that it's not necessarily 1/3 of the full available sugars, since certain yeasts won't be able to eat all of the sugar before succumbing to the rising alcohol levels. You'll have to estimate it.
You'll also want to aerate the must a couple times a day until the 1/3 sugar break as well since at that point you're trying to build a large healthy colony of yeast and they need O2 to reproduce. After 1/3 break is past stop shaking or stirring the must and let it become an anaerobic ferment.