There is probably a better solution to this...but, since Tableau can't dynamically generate parameter values yet, here's the best I can come up with.
For the date filter calcs in each data connection, currently you're comparing the dates in your actual data to the parameter values (I assume). So, one possible solution might be to have a new parameter called "Days In the Past Filter" or somesuch that defaults to 7. Then, change all your date filter calcs so that they evaluate whether there is a non-0 value for "Days in the Past Filter". If there is, then use that to perform the calc. If not, compare the date in the original data to the two other parameters, Journey Start Date and Journey End Date instead, and ignore the other.
I'd envision they'd be Boolean calcs that went something like:
IF [Days In the Past Filter] < 1 // 0 or negative numbers causes us to filter on Journey Start / End params AND [Actual Journey Start Date] >= [Journey Start Date] AND [Actual Journey End Date] <= [Journey End Date] THEN TRUE ELSEIF [Days In the Past Filter] > 0 // Positive numbers causes us to filter journeys that started no more than this many days ago AND DATEDIFF('day', [Actual Journey Start Date], TODAY()) <= [Days In the Past Filter] THEN TRUE ELSE FALSE
The end result would be three parameter selection boxes on the dashboard. The default would filter to the last seven days, and the user would need to manually set that value to 0 (or negative) in order for the two date range params to act as filters instead. It would be a little awkward and you'd probably have to include a little note in the dashboard explaining how to use it...but it'd work.