I am going to make up two sentences.
I want to talk to you about my travel plan later today.
I want to talk to you later today about my travel plan.
Which one is grammatically correct?
Both are correct. One is more clear.
The concept of "when to talk" and "what to talk about" are both adverbs modifying the verb "talk". If you put the "when" after the "Travel Plans" you introduce some uncertainty, because the travel plans could be made more specific by including a time that the plan is for. Maybe you're modifying the travel plans with "when".
You could eliminate that uncertainty by putting the "when" after "Talk" rather than "Travel plans".
So "I want to talk to you later today about my travel plan." is less ambiguous.