Ensuring that your server can deliver your website’s content whenever called upon is an important part of establishing the ability for any website to get rank.
Obviously, if users can’t access your site whenever they want, then probably neither can the search engine crawlers, and depending on how often they fail to connect to your content, they may simply classify your site as a ‘don’t bother trying’ address, spelling disaster for your business.
Most hosting providers will warranty your hosting server’s up-time with a reasonable service level, but I’ve discovered that it often depends on who the hosting provider is as to whether those up-time guarantees are genuine or very ‘loose’.
Generally speaking, if you’re paying good money for a hosting service, you should expect a 99% or higher up-time guarantee. That means the total time your server can be down is somewhere around the 3.5 days mark in cumulative total per year.
Some outages occur unexpectedly, but most outages are part of planned server maintenance.
Your hosting provider should advise you any time the server will be down for maintenance, and good providers will typically perform such maintenance outages during off-peak times. That said, there is no such thing as off-peak times for search engine crawlers, as they will typically visit daily and at random times of the day.
With low cost hosting services, you may encounter poor up-time levels. Avoid going with the cheapest option, it may cost you valuable traffic and consideration for rank.
There’s probably no positive rank benefit from having 100% up-time.
There is only likely to be a negative rank effect for having poor up-time levels, due to becoming classified by the algorithm as only suitable for intermittent crawling, and not suitable to provide positive user experiences.