Is the US certification process for airliners shorter or longer than in other countries?
Certification is just one part in the design process. Things like design or manufacturing issues can also cause significant delays on a program. Although much of the design is driven by certification requirements, it can be hard to determine whether the delay is due to regulations or just issues with designing for them. Estimating the cost attributed just to certification would be even more difficult.

Also, while the regulator of the country of design certainly is the primary concern, an aircraft must also be certified in any other countries where the type will be operated. An aircraft designed by Airbus, for example, will certainly be primarily certified by EASA. But to operate in the US, the FAA must also certify it. While the authorities do have agreements between them so that the entire process is not duplicated, there are differences in requirements and philosophies between the agencies. So if the FAA has some regulations that tend to cause the process to take a long time, it doesn't mean that Airbus is immune to those issues.

When a manufacturer applies for a type certificate (new or amended), they are also establishing a regulatory baseline. The new type must conform to all current regulations as of that date, unless they are able to negotiate something different with the regulator. This application is only valid for a limited time before the manufacturer must renegotiate.

14 CFR §21.17 (c)


  An application for type certification of a transport category aircraft is effective for 5 years and an application for any other type certificate is effective for 3 years...


While this is not a hard limit, manufacturers would rather avoid having to go back to the table with regulators years into their design process to extend their application and possibly have to step up to more strict regulations, especially for a new type.

Most recent Type Certificates from EASA list the application date and issue date. If the primary regulator is not EASA or JAA (predecessor to EASA), they list dates for that regulator as well.

If we look at recent designs, we can see that most new aircraft took about 5 years to certify, which would seem to indicate that there is no clear time advantage between regulators. This includes the A330, A340, A350, A380, 777, 787, CRJ, E145, and E170. For all aircraft not primarily certified by EASA/JAA, there was either only a minor difference in the time taken for each regulator, or EASA/JAA took a bit less time.

Amended types vary greatly, from much less than 5 years (A330-200, 777-300) to 5 years (747-8) or more (777-200LR). It is difficult to tell whether a longer process means a more complex product or a more involved certification process. EASA/JAA seems to always certify aircraft at the same time or after the primary regulator, but this is probably not due to the EASA/JAA process taking more time.

You mentioned Dassault as well. Although the business jet regulations and market are different from airliners, there seems to be a similar trend of about 5 years for new jets (Falcon 7X, Gulfstream VI, Bombardier Global Express, Embraer Legacy 500), and less for variants.