On and Until now

On adverb - Toward a point ahead in space or time.

Until now and on are semantically related. In some cases you can use "Until now" instead an adverb "On".

Until now adverb - Used in negative statement to describe a situation that has existed up to this point or up to the present time.

On and until now are semantically related. Sometimes you can use "On" instead an adverb phrase "Until now".