Most heart containers in Spirit Tracks are pretty easily obtainable. Some backtracking might be needed to get to the right locale if you miss a container, but that time required is pretty minimal.
There are some heart containers which are actually easier if you wait until later in the game, as you'd have more items/locations available, and be more battle ready.
With that being said, there is one heart container that could be a pain to wait on until later in the game. Without being too specific to respect your request for spoilers, it involves spending a certain amount of rupees at a single location before you are awarded the heart. Buying items from this location throughout the course of the game will allow it to restock. If you wait until the end of the game to attempt this heart, you could have a lot of downtime waiting to even be able to spend more money until it is restocked. Be sure to purchase the (very small item spoiler)
so that it will start tracking your rupees spent here.