Apologies for the delay in replying! We moved this forum into "Veeam nworks" recently, and it seems I did not get a notification of this post...I only found it by chance when browsing.
Anyway, the Snapshot Age monitor in nworks does not scan the datastore (this would have a big performance impact) - we get the age from the VMware API on vCenter. But the age should match the oldest 'snapshot' (*.vmsn) file in the VM folder on the datastore.
To your other question, if it takes 45 - 90 minutes for you to take a snapshot of this VM - then I think you could have a performance issue...perhaps a storage I/O bottleneck? I'd review what kind of storage you have, and how many VMs you are running there.
Vice President, Product Management