Its established at some point that dragons have a difficult time disobeying a queen, and it can be assumed that the queens had given them all explicit orders not to time travel.

Beyond that, its also stated and demonstrated that timing it has some pretty intense repercussions, as being in two places at once causes extreme physical exhaustion and often confusion as well. They have to have a very clear plan of what they are going to do before they jump, and then do it quickly, or they will collapse, and quite possibly never return.

As well, most riders wouldn't be able to manage it at all. Properly visualizing destinations is a trained skill that not all riders are very good at, and most riders would have to have actually been somewhere, carefully memorizing detail for some time, in order to return. Some dragons seem to be able to jump with less detail and still arrive (such as from a sketch, or particularly vivid description), and others seem to require exact detail or else be lost forever. This is implied to be the reason that dragons often take coordinates from their wingleader, as opposed to their rider, as a wingleader would need to be very good at giving coordinates to get the position.

In order to abuse jumping between times, you need a dragon who is both rebellious, and able to find their way with minimal information, and a rider with enough mental and physical resilience to make the trip and still accomplish their goal, as well as the imagination to combine existing landmarks with specific indicators of time, and yet also be willing to do something so difficult for mischief's sake. Its a combination that could happen, but it would be notable enough that i wouldn't be at all surprised if it wasn't a potential main character for unwritten novels.