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?
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2019-06-14T10:21:44.777
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grammar particles particle-に particle-で に-and-で
Why is に marking time and not で？
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
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2019-06-14T13:08:58.970
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answer
My conclusion:

Time can also be a target of a verb. The target is for the verb to be
performed at the time marked by に. It is not just part of the context around
the verb (the place where the verb happen, the means by which the verb
happen...) therefore で is not suitable.

for example:

> 「2020年に日本に行く」

The target of 「行く」is to go to Japan and to be there in 2020. That's also why
omitting the に from the time means this is no longer the target of the verb to
be performed at that exact time, so it turns to be just part of the context.
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