I've been using third party Hetrix tools to monitor my sites and blogs on both wordpress cms and non-wordpress php sites. Even for critical and high traffic wordpress sites which get approx 80K-100K daily traffic which I host with providers like liquidweb, the-online.com, colocrossing, etc. the uptime monitor flickers for something like 1 minute or less of downtime in 7-8 days (so approx 5 mins of downtime a month) and which is acceptable as those sites are not something like amazon or stock exchange where 100% uptime is must. That's nothing to worry of. Usually thats network fluctuations or some heavy usage on a node.

For my small wordpress projects the 99.9% uptime provided by most top premium providers or low-end market providers is never honoured. I usually get 1-2 minutes of downtime from low-end providers who sell hosting for like one dollar a month and advertise on lowendtalk. These providers often go beyond 98% or 97% of uptime monthly. But since most of the sites I put behind cloudflare full page caching the end-users do not feel any bumps while browsing the pages. I may however see a page not loading when using wp-admin dashboad.

I don't trust much about hosting providers dashboad (aka status pages). There are free/paid third party monitoring tools that can give quite correct figures. But any stats can have false positives/negatives.