I agree with hanna below, if your using fluch niacin that will be too much to start. The flush is caused in part by a histamine dump and your body will replenish histamine rapidly.
With the above in mind you dont want spacing between large doses to be too far apart because that gives the body time to build up histamine and the flush will be severe.
This is why you want to dose 3x a day. starting at 100mg or so each dose and working up by 50-100mg at each dose over the course of weeks.
The first time I popped 500mg I thought I was going to burst into flames, not fun at all! Now 100mg doesnt phase me as long as I dont miss a dose.