maybe the coinbase maturity was what you meant?
No, because it was 120, before it was simplified into 100. If you have 6 blocks per hour, then 120 was used as "20 hours".
After a block is created, the maturation time of 120 blocks is to make absolutely sure the block is part of the main chain before it can be spent. Your node isn't doing anything with the block during that time, just waiting for other blocks to be added after yours. You don't have to be online during that time.