Season 5 in Overwatch should start sometime around June, but it still hasn't been confirmed though. Seasons in Overwatch usually last about 2-3 months and 7 days if it's mid season.
We still don't know the exact changes that are going to happen in season 5 for Overwatch, because the new season just started, but the CP rewards will be the same:
Grand Master 3000
Top 500 had some major changes too, now you need to stay in top 500 when the season ends to get awesome rewards.
Before that, you just had just to reach the rating and you would've gotten the spray.
And there is also skill rating decay. If your rating is above 3000 you need to play 7 games per week to maintain your rating or you will start to decrease.
When you complete a match, the amount of time until skill rating decay occurs is pushed back by 24 hours, and you can bank up to seven days per week. That means that as long as you manage to play seven games over a one-week period, your skill rating will be safe. You could play one match per day or complete all seven in a single session. It’s up to you.
If you don't have time to play the one game in Overwatch we can do it for you.