にわたって and its variations emphasize that the activity covered a long (or longer than expected) period. In English, the nuance is something like this:

I studied for three hours.

 

I studied for three whole hours.

I feel like にわたって also has somewhat of a formal/written sound to it.

A reference: Learn JLPT N2 Grammar: にわたって (ni watatte)

にわたって and its variations emphasize that the activity covered a long (or longer than expected) period. In English, the nuance is something like this:

I studied for three hours.

I studied for three whole hours.

I feel like にわたって also has somewhat of a formal/written sound to it.

A reference: Learn JLPT N2 Grammar: にわたって (ni watatte)

にわたって and its variations emphasize that the activity covered a long (or longer than expected) period. In English, the nuance is something like this:

I studied for three hours.

I studied for three whole hours.

I feel like にわたって also has somewhat of a formal/written sound to it.

http://japanesetest4you.com/flashcard/learn-jlpt-n2-grammar-%E3%81%AB%E3%82%8F%E3%81%9F%E3%81%A3%E3%81%A6-ni-watatte/

にわたって and its variations emphasize that the activity covered a long (or longer than expected) period. In English, the nuance is something like this:

I studied for three hours.

I studied for three whole hours.

I feel like にわたって also has somewhat of a formal/written sound to it.

A reference: Learn JLPT N2 Grammar: にわたって (ni watatte)