Regarding army service, anyone learning full time, or even almost full time. http://www.hebrewbooks.org/pdfpager.aspx?req=13429&hilite=7d9e56c3-9558-4c55-bb40-f52a65157dc2&st=%d7%9e%d7%9c%d7%97%d7%9e%d7%aa+%d7%9e%d7%a6%d7%95%d7%94&pgnum=293 [or <http://j.mp/OoSZG4>, this particular essay is by R YM Tikuzcinsky.]