Well, first I doubt that five carriers could have been at Pearl Harbor in December 1941 based on current US dispositions of their fleet. The Wasp, Ranger, and Yorktown were all on the East coast with the Atlantic fleet at that time.
The Lexington, Saratoga, and Enterprise were operating out of Pearl. The Hornet was still working up in local ops on the West coast having just barely being completed and put into commission less than 60 days before (27 October 41).
Other than this, the US had a contengincy plan in place as part of War Plan Orange for rapid conversion of large merchant ships to carriers under WPL-10. These merchant ships, mostly liners, refered to as XCV, were to be taken in hand, converted, and re-commissioned as carriers from M+90 to M+360 per the above plans. Conversions included a total of 10 liners in 1941:
California, Pennslyvania, and Virginia of the Panama-Pacific line (turbo-electric, 18.5 kts 600 ft, 30,250 grt)

Manhattan and Washington of the US Lines (steam turbine, 705 ft, 21 kts, 32,000 grt)

Mahlolo, Mariposa Lurline, and Monterey of the Matson line (Steam turbine, 20 kts, 632 ft 31,000 grt)

President Hoover and President Coolidge of the President Line (Steam turbine, 654 ft, 21kts, 31,000 grt)

These are all far larger and more capable designs than the two Japanese liner conversions, Junyo and Hiyo. First, since the late 20's the US Maritime commission had some input into these ship's design such that they were from the outset designed in part for this conversion. The 1940 - 41 P4P merchant hull which was to replace these ships for conversion was actually designed with not only conversion in mind but actual military features like a split plant.

As converted it was expected these carriers would have an air wing of 55 aircraft (27 fighters, 18 dive bombers, 15 torpedo planes) and an armament of 8 5" 38 guns and up to 40 .50 machineguns. So, they were nearly the equivalent of fleet carriers except in speed.
This would mean that the first conversion, if rushed (as likely would have been the case) could have been in commission by March or April 1942 with roughly a 60 day work up before deploying in May or June of that year. The planning had an additional carrier conversion per month (roughly).
If the US was desperate for carriers, there is little doubt this plan would have been executed in short order to take up the slack until the Essex class could begin to be delivered.
Japan has absolutely no equivalent to this. They lose their air wings or carriers, it will be a full two or more years until they can put another one to sea.