Shooting from the hip, I would guess one of your new capacitors has failed. A delay like this is consistent with a leaky cap taking some time to get charged. Is the delay getting longer? If so, the cap is probably on it's way to never charging fully and A600 to never booting.
Not sure people realise. You can actually boot your amiga with no electrolytic caps attached (except the main 12v rails). Obviously, running it like that for a long period of time would be silly.
