Without wishing to sound obvious or unhelpful, it really is sufficient training to pass the tests. If you're up to speed with light singles and twins then you can cut your air time down by studying the relevant country's procedures. In the end that's what it boils down to for experienced pilots. I assume you will have to do a commercial flight test - in a complex single - and an IRT. If you haven't flown either for some time then get some practice before you start paying fortunes for the commercial training.
The CPL flight test will include a VFR nav section, this may be the only difficulty if you're out of practice. The rest should pose few difficulties provided you take on board the local procedures, particularly test procedures.
I'm sure you know all this and all you really want to know is how long? Well I wouldn't listen to anyones suggestion until they have flown with you. But as a guide, it has been done in as little as under 5 hours and as much as 30 or more!
Not much help maybe.
Good Luck
Ivan