Question: when to use buong araw vs maghapon?

"Buong araw" means you've done/felt something the whole day.
"maghapon" is only used if you have done/felt something past noon.if you are using maghapon.
you can say it like this:
"Maghapon siyang pagod dahil sa ginawa niya kaninang umaga."

that's what I thought but when I put your example in google translate, it translates to "He's been tired all day because of what he did this morning." I've also seen it used in other sentences meaning all day. Is there another rule of using this that doesn't make it relate to just afternoon?

Pwede ba? Napagod siya sa buong hapon.

As a native Filipino/Tagalog speaker, I think that both mean "whole day." I don't think there is a "strict" translation for those words.When using "buong araw" or "maghapon" in conversations (particularly casual conversations) with us, we would understand it as "whole day." We use it often, and we interpret it as "whole day." What I mean by whole day is from sunrise to sunset.The word "hapon" means "afternoon." So sometimes, when we hear "maghapon," we interpret it as "whole afternoon" especially if the context of our conversation is about afternoon. But generally, "maghapon" means "whole day," from sunrise to sunset.There is no "perfect" translation. These two languages have different language rules.

@LiamAdlerPH Thank you so much!

@LiamAdlerPH
Thanks for your input!@kuya19 I'll just add, it's really important not to rely on Google Translate to explain language nuance -- it's just not intelligent enough in many cases.

@LiamAdlerPH That makes sense. Thank you!