Yes, premine is basically a few high reward blocks the dev solomines before releasing the coin (wallet, source, etc).
Instamine is when blocks are mined way too fast than what was intended; let's say the block target is 60 seconds, so 1 block should be mined roughly every 60 seconds. There's a mechanism in place that controls the complexity of solving the next block (based on how fast blocks are being found by miners), called difficulty retarget. Which make blocks harder to mine if blocks are mined too fast and vice versa. Coins are almost always launch with very very low difficulty and it takes time for the difficulty retarget to increase the complexity of solving blocks by a huge amount and when a coin is launched, a huge amount of miners will start mining while the difficulty is only slowly climbing.
Instamining can be as fast as mining hundreds of blocks within minutes. And can last a long time, depending on the difficulty retarget in place.
Alright thanks.
Therefore what would be an appropriate amount of % for premine?