Aggregate Metrics (SUM) changes on period change in Cloudwatch.

There are two time periods to configure. The one above the chart is the time period that the chart will cover. The one above the metric, labelled "period" and next to "statistic" is the sample period over which the selected statistic is applied. In your use case this is sum over either 5 minutes or one hour. When hovering over the chart you're shown the time slot and the metric value over that time slot. If you move left or right you'll see a different time slot with it's own corresponding value. So if you change from a 5 minute to a one hour sample period, assuming your data is evenly distributed, you'll see a 12-fold increase in the sum. Changing the chart time period - the one at the top - will just show more of these 5 minute or one hour samples, but won't change the aggregation.

The aggregation period can be set up to 30 days if that helps? There's the option of downloading the data as CSV if you need more control.