Time in Rocking Soccer passes faster than it does in real life.
Each day in the real world corresponds to a week in Rocking Soccer time. There are 52 weeks in a season, so a season takes 52 real days, a little less than 2 months.
During this period, you will usually play twice against each team in your league. Depending on the league size you'll have between 30 and 39 league matches per season. Besides the league matches you may play friendlies, cup or international matches.
Some (real life) days are reserved for matches of the national teams. No club matches are played on these days. You can play friendly matches, but if you have internationals in your team you can't use them on these days. League playoffs can also be played on these days, so you won't be able to use your internationals for all of these matches.
Between two seasons there is about a week in which no league matches are played. In this period, the playoff matches are played for promotion/relegation to higher/lower league levels. If you don't play any promotion/relegation matches, some friendlies matches will be scheduled for you.