Critical - P2 The normal Free Monitoring metric interval is 60 seconds, and this is honored by mongod for the POST interval for ongoing metrics. However, when mongod first registers with Free Montoring, it sends a payload of up to 10 metrics that were previously buffered. The interval for these metrics seems to be 1 second, rather than 60 seconds.
You can see this in the timestamp suffix of the metric _id in the Free Monitoring DB:
> db.metrics.find({_id: /MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==.*/}, {_id: 1})
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338552006" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338553010" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338554008" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338555011" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338556009" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338557006" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338558006" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338559006" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338560006" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338561006" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338562006" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338622005" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338742010" }
{ "_id" : "MSA0YjdhMWZkOS01NzMyLTQ2NTctYWRjYy03YmRiYjZkMmUxZmIgTlp0OVdDcGh6YVo0bldXSGQ0MUJyeCtLWWxZSFYvVkFxNk9DQncwREwwUEp0WElPeklCdEErSlpPM0l3N2NValpxR0NGa1RyTlNsWkY3SFZPK1pia1E9PQ==-1529338802010" }
Notice that the first batch of timestamps are 1 second apart (although oddly it seems there are 11, not 10?), and then 60 seconds apart.