When to add nutrient and energizer

When to pitch nutrients, which nutrients to use, and how much is rather lengthy. Therefore I will direct you towards chapter 10 of the newbie guide:
http://www.gotmead.com/forum/attachment.php?attachmentid=1300&d=1395107426
Although, I'd be careful with the phrase "Using nutrients is not an absolute necessity", especially in a newbie guide. It takes quite a bit of experience or specific recipes (JAOM) to avoid the use of nutrients. My personal short answer would be: I pitch nutrients around two hours after I pitch the yeast so that it's during the lag phase. EXTRA: I think the absolute latest to add nutrients/aerate is the 1/2 sugar break, but you might want to aim for the 1/3 sugar break

- I wouldn't pitch the nutrients while the must is still hot as this may be detrimental to the vitamins present. There is some discussion on whether or not to boil in general, and it seems the majority agree that you usually can do without boiling in most cases (and would possibly be better off).
- You can also check up upon staggered nutrient additions (SNA) for a more "advanced" read. This is optional in many ferments, but SNA is never bad.
- Needing a yeast starter is also a possibility, but I never used a starter with my dry yeasts

Maybe after yeast pitch, once there is sign of active ferment.

If it's staggered addition, there is an academic paper (sorry, no link, and yes I'm still looking for it again) that says if you work out how much you need to use, then for the first addition it can be up to 85% of the total, then the rest should be added by the time the ferment reaches the 1/3rd sugar break......

That is a pretty common way to add them. As soon as you see signs of bubbling, you can add them. Folks here often stagger the nutrients and will add 50-75% of the total amount at that time, and will add the rest when the yeast reach the 1/3 fermentation point.

I know there is good reason not to use nutrients when rehydrating your yeast, but is there any reason not to add the first round of nutrients right up front with the yeast and oxygen if you're pitching liquid yeast or already rehydrated dry yeast? I've always done it that way and things have worked out well, though I can't compare to adding the nutrients later since I never thought try that. What advantages are there to waiting?

There is more than one way to skin a cat.

It is OK to use rehydration nutrients (like GoFerm) when rehydrating. You just don't want to have DAP or ammonium ions in the mix.

There are some theoretical advantages to adding nutrients after the lag phase, such a not feeding wild yeast or potential spoilage organisms until the yeast colony has had time to reach dominance. There may also be some increased division of cells and less growth in size of individual cells with yeast that are somewhat nutrient hungry early on in the process. I don't think there is any evidence that waiting makes better meads. Typically I will add nutrients to the must and then pitch my properly-rehydrated yeast.

I'm somewhat lazy when I do mine and tend to frontload everything either at pitch or when I see signs of fermentation. One of these days I'm going to actually do a batch with SNA's, DAP, Fermaid, Energizer etc. Despite not using SNA on any of them, using only boiled bread yeast for some purely organic batches, and front loading energizer & fermaid I have been having some rather tasty ferments. Some never made it to secondary (two legged cellar rats keep attacking!) they were so good. Others are needing the regular time (1 month/ABV %) to age.