Staggering won't change the aging process much from what I've been able to see, though making sure enough nutrients (in total) are there does make a difference. The faster ferment needing longer aging rule is often true, but the primary driver of that is fermentation temperature. Higher temp = faster ferment = longer aging. This not, however, an absolute rule as I have made delicious mead that only need to age for a year that was fermented at 84F, but few recipes will do that. Using nutrients may lead to faster ferments (taking weeks rather than months), but well-nourished yeast produce fewer off odors and flavors, and really long ferments may be prone to higher acetic acid levels. So proper nutrition = less-aging-required in many cases.
While there is no specific point at which you must add nutrients, you'll probably see better results if you get them added in during the first 1/3 of fermentation. Adding 1/2 of the nutrients after lag phase (when evidence of fermentation first becomes visible) and adding the the other half at the 1/3 fermentation point works pretty well. To determine the 1/3 fermentation point, assume your final gravity will be 1.000 (this works in most cases, except for very high gravity musts). So it you start with a gravity of 1.100, the 1/3 fermentation point is 1.067 (the half-way point would be 1.050).
It isn't crucial to hit these targets exactly, but being in the ballpark is good. If you wait too late, the yeast become unable to assimilate ammonium nitrogen and the nutrients won't be much help.