for all the things onyx does (or, for that matter, doesn't do), there's no reason it should shorten your boot time. it's good for what it is, nothing more (or less).
It tells me my disk needs to be repair. (Hold cmd + r at boot) but this brings me to "Internet recovery" with ML.
How else do I repair the disk?
Is that Onyx telling you or something else?
Again, you shouldn't use Onyx to maintain your mac. OS X does NOT need maintenance since it has its own maintenance scripts that it runs automatically. Maintenance apps might do more harm than good and it might have bugs that might give you wrong information. Unlikely, but still possible.
Anyways, here is what you need to do:
Step 1: Ditch onyx.
Step 2: Open up Disk Utility and click on your Hard drive icon on the left and click "Verify Disk" or "Repair Disk". If OS X indeed reports that the disk needs to be repaired then:
Step 3: Backup.
Step 4: Then shut down the computer, hold CMD+R while booting up. In recovery mode, you should be able to use Disk Utility to repair the disk. If it's successful, then no need to worry anymore.
Is that Onyx telling you or something else?
Thanks. Onyx was telling me it needs to be repaired.
When I hold down CMR + R - It starts with Internet recovery and looks like it is downloading ML install?
But I will use disk utility first to see if it reports errors.
Maybe try this instead: the next time you shut down, hold down the Option key instead while booting up. After the gray screen, you will be presented with a bunch of hard drives. Select the "Recovery HD". Once you go into that, you should be able to see Disk Utility. Click on it and click repair disk.