I sometimes play two octaves at once when playing melodies but recently I discovered a nice sound when I play them sperately with a slight delay. Whats the musical term for this?

Un-coordinatedness...

lol, you've hit the nail on the head there Kurk.

I suppose you could call it a "Russian" arpeggio too.

I'm not sure there is a term for that, but if you ALWAYS delay the melodies, it will soon sound chaotic. So, don't overuse it. Unless, you are taking about a fugue, then, in that case, the two subjects are going to different directions.

the term you search for is 'eco'.

In music training they consider playing two voices using two octaves very bad form. Although, a composer had once told me that "there are no rules, anything that sounds good is good." Just be careful, for this practice can sound, as mentioned above, a bit chaotic. I would use the term "empty". In typical musical harmony training, they recommend that "consecutive octaves" be avoided. Yet, there are some pieces comprised with them to deliver a certain effect, so they cannot truly be classified as wrong.

As for the slight delay when playing the octaves resulting in a different type of timbre, there is a technique that is similarly used on the guitar called bowing a note, coming from the effect of a bowed not on the violine. I am not sure what pianists call it.