The time error shows up when the RRDs have an update time in the future of what the AMP time is (with a 10 minute leeway for this). There's a sanity check during nightly_maintenance before creating the backup that verifies the time stamp of the RRD compared to system time.
[root@amp mercury]# cd /var/airwave/rrd/
[root@amp rrd]# cat rrd_check | wc -l
For a server that's performing optimally, the rrd_check file should be empty (above command should yield '0'). If you see a large numerical value, then you most likely want to get support involved.
I think with the number of RRDs you have, it's probably taking over 10 minutes to check through all their time stamps, this means that the files are already updating to the current time stamp with current data post nightly_maintenance start time, which may be the reason you're seeing the error. A good way to check how long it takes to run through all the RRDs is to run this command:
# cd /var/airwave/rrd; time find . -type f | wc -l
If the time exceeds 10 minutes, then you'll want to get support to patch your system.