Time skew errors?

I've been getting an intermittent spate of this sort of error lately:

Expected(200) <=> Actual(403 Forbidden)
excon.error.response
:body => "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<Error><Code>RequestTimeTooSkewed</Code><Message>The difference between the request time and the current time is too large.</Message><RequestTime>20181015T210406Z</RequestTime><ServerTime>2018-10-15T20:48:43Z</ServerTime><MaxAllowedSkewMilliseconds>900000</MaxAllowedSkewMilliseconds><RequestId>9379DD3E544E87CF</RequestId><HostId>LvBdMDIwvhP1X/jMpfYIaBjZ24h1EmgkU3ZZ+0s+JtaPfWPSlxMQLCoGL67H1C+kIkgMw2u1gtI=</HostId></Error>"

So this tells me that my server is set to ignore any form input that is more than 15 minutes stale. I could raise the limit (presumably this is something that is set via a config), but what hazard is this exposing me to?

Walter