Why is に marking time and not で？


As I have learned, the に particle is marking the target of the verb. And it
make sense for most cases I have seen except for time. How exactly can time be
the target of any verb? Wouldn't it make more sense if it's marked by で which
gives us context on the action?




Target of the verb is one of many usages of particle に. It is also used to
mark a place, a point in time, originator of action in passive sentences and
more  
While dictionary is not a primary source for grammar, for starters you can
check out <https://jisho.org/word/%E3%81%AB>  
So marking a time is simply within a scope of what に does.

That said: で is also used with time words. As far as I know this gives the
nuance of "by (the marked time)" and that に has a nuance of a more exact time
in comparison

