The unknown will be how much studying do you need for the writtens and to get ready for the commercial checkride. There's TSA madness that I know nothing about. If you have your CAA verify your license to the FAA you can get the FAA private in an office visit. Call it an hour. If you have the FAA IR written results in hand when you get the private you'll get a private with the IR. The IR written will take a couple hours. While you're at the testing center you should do the commercial written, another couple hours. Now it gets complicated. There is a requirement for 10 hours of instrument training and 10 hours of training in ME airplanes (I'm assuming you want a commercial MEL.) And there is a requirement for 3 hours training with a FAA CFI within 2 months of the checkride. How much of the 2 ten hour blocks for training you can document out of your logbook will vary.