Hitters struggling with timing isn't anything out of the ordinary, especially at the beginning of a season.
Because of the individualized nature of timing I look at timing as a skill each hitter needs to develop through a set of exercises or skill developing activities like the drill from the video above.
This hitting drill is a very simple hitting drill that helps hitters work on their timing skill and has helped many hitters I've worked with get back on track.
If you're a parent, hitter, or coach I would also recommend reviewing this post I made on the fundamentals of the swing.
Timing issues are often accompanied by mechanical issues such as the hitter not getting to the proper launch position, improper sequencing, or poor bat path.
If you're looking for additional help feel free to email me at firstname.lastname@example.org. Always happy to help in any way that I can.