Cloudwatch metric gauge on weekly base

Within CloudWatch dashboard, I have a gauge metric which shows the sum of a custom metric (custom metric represents the number of log entries over time). The number of log entries is very consistent per day (lets assume 8).

I'd like to only include/show data since the last Friday. So on a friday, gauge should drop to 0. When I configure to show the last 7 days, it shows every day nearly the same number (8 * 7 = 56).

Expected example:

I tried with MATH "if", but there is no NOW() function. Does someone have an idea how to achieve this?