Depending on your use case, you can either provide a default value of the combo-box with the filter most of your users are going to use, (e.g. like To and From date if this is some ticketing site). You can also have a not-selected drop down that enforces user to select a value before you show next options to the user. This is useful when you want user to make a conscious and explicit choice.
Currently your view involves accordions. I do know exact purpose of including that as that component is taking much of your real estate which can be used in a better way. I can have a small box which has filter selection combo followed by single value or multiple value selection choices and a bigger content area to show the results.
If I am correct then you are building a filter which can make use of deferred create. Currently, your form is not telling me what I am filtering. I mean Interval of X and Y of what? Amount, date, locations? You can include that information at the top of your form too.