As others have noted, there are tons of factors that influence the frequency/depth of a validation. IMHO, if you're doing it independently for the first time, your best bet is to go with a two week job (100-120: 80 hours + overhead) with roughly one week budgeted for assessing data management, one week for assessing system settings (e.g. rule parameter evaluations, etc.), and some time in each to assess governance controls.
If you're doing it annually or even bi-annually, you could probably pass with a one week job (50-70 hours total: 40 hours + overhead) with the scope dependent upon your combination of core and AML system. Some AML systems have really robust controls for data integrity and can allow the independent validation to be more focused on the system's ability to detect suspicious activity; others it's the reverse. Some AML systems are awful on both fronts and need a ton of validation work. It all depends.
Also, of course, if your Bank has any major system changes, it's not a bad idea to validate both internally and externally thereafter.