After some regtest and after being in shame for guilt to Usetup, I found why ReactOS takes up to 20 minutes to pass away the CheckDisk page in 1st stage.
My partition scheme is as follow:
1st 20GB contains Windows 2003:
Primary, Boot, System, FAT32
2nd 10GB contains ReactOS for testing
And one logical partition with 80GB but it does not matter for this.
Both primary partitions are formatted with the Windows Server format Utility, so I can access to ReactOS files from Windows and vice-versa, because you maybe know Windows cannot access to FAT32 partitions formatted with ReactOS.
Well, the problem starts with r70792, in which for some reason ReactOS does not recognize as valid the partition formatted from Windows 2003, and takes 20 minutes trying to repair it and then proceed with the file copy.
Here I've attached two debug logs,
20170106_011609.log with 70791 (normal behavior)
20170106_003213.log 70792 (regression),
with a quick view I can see where is the fail, but better devs can see more info.