This is not necessarily a built-in in Sage. You can use matplotlib directly, but either way it looks like it might take a little extra time. See this stackoverflow question for a good example of how to proceed. The first thing I would suggest is to find a way to get your dates in Python datetime format. This stackoverflow question has the good suggestion of
sage: from dateutil import parser

In Sage the problem will be getting the circles to plot, because they will not accept datetime instances for coordinates. But you could use the parser above to create a tick formatter that would work - see here for one of many examples of such formatters. Sage should accept any matplotlib formatter properly in the tick_formatter argument to a plot, though again you may have to do something inventive to pass in just numbers rather than datetime instances.