Skipping time is one of the most dangerous things you can do as a writer. While it can be necessary, it very rarely is, and when it isn't, it can be one of the worst ways of betraying your audience.
Probably the worst one I've ever seen was in the beginning of the book The Grace of Kings by Ken Liu. In the first chapter, he introduced to me a protagonist that I honestly really, really liked and wanted to see him do great things and overthrow the oppressive government. But guess what happened in the beginning of the second chapter? Surprise! It's seven years later and he's a completely different person now! I would never see that fun character in action. Even worse, nothing in that first chapter even ended up being important. I would have dropped the book right there if I hadn't still liked the new Kuni.
An example of a good time skip was in Attack on Titan (the anime, not the manga, where it was handled just shocking badly). After the first two episodes, where I was met a protagonist I really liked, who had both sympathy and admiration points in plenty, the main characters had to go through five years of training, so they mostly skipped it. There are two reasons this is okay: first, they do include two episodes about the training, which made me feel that I hadn't missed out on anything major, and second, no significant character development takes place that you don't get to see.
So those are the two requirements you have to meet at least one of when you do a time skip: either don't significantly change the characters over the skipped time, or show some excerpts from it. If it's a long time you should probably do both.