This is a direct answer that doesn’t soften the topic, because the sooner you connect with the facts, the better, in my opinion.
Here is a page of apps from Sadhguru, who is a truly wise enlightened person: Sadhguru & Isha Mobile Apps. Sadhguru was enlightened more than 30 years ago, and has been working continuously since for what is necessary for humankind. Now, they have touched millions upon millions of people and have a huge volunteer base backing these apps up.
YouTube also has an app.. and you can find so many high quality meditations in YouTube. One channel from YouTube is channelhigherself and contains around 2000 top notch videos, with pure energy and great wisdom. You can listen and watch these videos in a mobile browser or YouTube app, most of which contain teachings with guided meditations built-into them. Almost all of them are free and their overall energetic quality is the best I have found.
How frequently you should meditate? Beginners are often given a duration of 5 to 20 minutes when they are beginning. This is an introductory time. You can meditate as often as you want. Check out this article from an enlightened person (creator of channelhigherself) for an accurate/conscise framework to start.
Actually though, answer this question: How often is to your greatest benefit that you live in truth? That is the best amount of meditation that you should maintain. I know this sounds rather extreme, but the sooner one sharpens one’s focus to truth and commits to living it moment to moment, all the time, the better.
But.. this can be misunderstood. You must not see truth as a goal to be chased. You already asked what you can expect from meditation. The truthful answer is: nothing. Meditation is losing who you think you are in fact. It is losing everything that you think you are. So, it will give you nothing, but take you (who you think you are) away. Then truth will remain. Truth was always there, but it was covered up. Meditation will take the cover away. This doesn’t mean the body will die. You were never the body anyway, so meditation won’t take your body away. In losing the illusions, who we truly are is uncovered. We don’t gain anything. The perfection that already exists as us is uncovered more and more.