Question: We're creating a chart showing traffic by time of day over a given period. So the y-axis is traffic, the x-axis is midnight, 1am, 2am, etc. It could also be days of the week. What's the generic name for this type of chart? I've come up with "cycle chart". Is that the standard? Is there one?
![example](https://i.stack.imgur.com/IDu3k.png)

Update:

Just to add a bit more clarity, what's being shown in the top chart is *not* one day, it's an aggregation of many days. E.g. over the last month, 6am has on average been lower than noon. Similarly, in the bottom chart, over the last year, traffic dips on Saturdays.

Answer: 
What you've illustrated is a time series column (or bar) graph. The two graphs are of differing time resolution or differing time aggregation. 

There may be industry specific terms for these types of charts. In finance, for example, the [open-high-low-close chart](http://en.wikipedia.org/wiki/Open-high-low-close_chart) is a very common time series plot:

![enter image description here](https://i.stack.imgur.com/2eiG2.png)

When the x axis is time, as in your example, it's often common to illustrate the points as a line graph, instead of bars/columns. The reason for this is to put the visual emphasis on the change from one period to the next. 

You might also consider graphing period-over-period. For example a [year-over-year](http://spotfire.tibco.com/community/blogs/stn/archive/2009/01/28/create-a-year-over-year-comparison-chart.aspx) would show how the numbers for a given month (typically, although could be month or day) compare to the numbers of the prior year for the same month.

![enter image description here](https://i.stack.imgur.com/nrlo1.png)

But I realize your question was about naming, not all the other cool graphs you can do ;)
Your charts are a diurnal hourly-average bar chart, and a one-week daily-average bar chart, respectively.