Well, the better way to look at this instead of I need this many tsp would be to look at how much YAN you need. ( This is what you are adding when you add nutrient.. that and vitamins).
Based on this
http://www.brsquared.org/wine/CalcInfo/HydSugAl.htm
and this
http://www.nanaimowinemakers.org/Winemaking/General/AddingNitrogen.htm
I would shoot for 300 mg/l (ppm) YAN broken up into 3 steps. Once at the end of lag phase, once at the 1/3 sugar break and once at the 1/2 sugar break ( since you are using DAP).
http://www.winemakingtalk.com/forum/f86/got-off-phone-fermaid-people-38704/index7.html
So, on the end of the linked thread I list a generic equation that I scratched up that defines how much nutrient one needs to add from a set of mixed sources to hit a certain YAN target.
mg/L YAN (PPM) =(.10*(mg/L) fermaidK +.04*(mg/L)*FermaidO+.2(mg/l) DAP)
Since you are using DAP the equation simplifies down to
mg/L YAN (PPM) =.2(mg/l) DAP)
300/.2=1500
Thus you need to add 1500 mg/l ie 1.5 grams per liter or .5 grams per liter if you breaking this up into 3 steps.
So taking that you have 19 liters 5 gallons is around 19 liters.... you will need a total of 28.5 grams of nutrient in total drawn out in whatever how many steps you plan on making.
However, something to consider is that it is doubtful that either of these products are just pure DAP so, if you are worried about hitting legal thiamine limits you might not want to exceed the max recommended by the manufacturer. However, this how much should be needed for a nice healthy fermentation.
One of the reasons why I like Fermaid O is that it does not contain thiamine in it, so I can add however much I want to add to my mead and it is no big deal... So generally, I will do a mixture of Fermaid O and K, using Fermaid K up to that limit I was talking about and then going the rest of the way with Fermaid O.