... planning ...

[Odessa Dawn]

Spending a lot of time planning is major procrastination.

Is that grammatical and natural English?

 

[Skrej]

It's okay, although you could also stick in an indefinite article before 'major'.

It's not the most natural utterance, but it could work well in certain contexts.

 

[andrewg927]

It's not natural because we usually don't think of planning as procrastinating.