I don't know how often ADS squirts it's reports out.
The Enhanced Squitter function on an ADS-B aircraft seems to send out a position message every second or so from my observation with personal receiving equipment. This is a passive function, does not need to be 'interrogated' as with mode 3. I believe ADS-C (or ADS-A) generates position reports less often but sends them through the satcomm link.
Maybe Shore Guy is still lurking here, he has worked for years to bring ADS-B online and we all owe him for his efforts to make us safer.
If the wreckage is never found, the stream of messages on ACARS, HF, and ADS-B and/or ADS-C may well be our best hope of understanding this mishap.
Since ADS-B transmits at 1090 MHz and is line of sight the only record of AF447's final minutes may come from a surveillance aircraft or satellite which might be a long shot. When Delta had a near miss out over the Atlantic in 1987 recordings from at least two military aircraft helped sort out the aftermath at the hearing.