instamine = dev mines at low difficulty before anyone gets a chance to, usually while pretending theres no premine or in combo with high rewards for early blocks. its just means that you plunk so much hash on the coin that difficulty doesnt have time to adjust, so blocks are found almost instantly (or at least way lower than the target time)
premine = dev starts out with, well, premined coins

i think you mean ninjalaunch, not ninja mine.
ninjalaunch = dev starts the mining process without giving advance notice, or maybe he does but doesnt provide a countdown to exact time