When the IDE prints the size of the compiled sketch is when to release the reset switch.
After much trial and error i finally succeeded, mainly due to the above.
I'm not sure if CP210x has the DTR signal, but the cheapo module i have doesn't (may try to hack it later).
I'm not sure what you mean by 'timing bethod', but sketches on the 328 would print to serial just fine.
Also, because i was also testing using the AVR-ISP for flashing (added a new board to the boards.txt), it would nuke the bootloader and as such there would be no way for the upload to succeed using serial until flashing the loader again.