It's a bit dangerous to declare that you will save a lot of time by using O/RM instead of writing manual data access code. There are situations when you won't, but when O/RM fits well, it can save a lot of time and free up resources that can be put on the core logic instead of the data access logic.

During work on a large application I made the following observation. When I needed to make a change regarding data access that only affected the code using the O/RM, it was done radically (almost a magnitude) faster than when I needed to make a similar change to code where manual data access code was used (because of optimization).

But before you see that potential save in code/time, you do of course have to pay a learning curve. Nothing new there. All new tools/techniques have a learning curve that will kill your productivity for a while, but hopefully you will come out and be more productive than when you started.