It does not take weeks to synch the FDR to the CVR. And at that I will exit stage left...
Although a "quick look" is likely just a few hours for the CVR the FDR probably will take a bit longer.
Have lost the link (buried many pages back) to a DFR problems report that discussed the dismal state of the documents that link the raw bits from the DFR to measured paramaters. It also discussed the typical process and problems with using the data:
Before using the DFR data it must be carefully checked to ensure that the calibration values are valid since there have been many instances of wrongly documented "gain/offset" valies or calibration drift after last inspection (which are also inadequate), not to mention totally incorrect channel to parameter maps.
This vetting is in partdone by comparing all 30 hours (or whatever it is) of normal operations to retrieved values - flap position on take-off etc).
Only after this is done can the CVR be synchronized to DFR tracings in a meaningfull way.
I suspect that is where most of the "weeks" will be spent the actual time stamp linking as you point out is very quick.