1. After the form is open you can  set it to visible False

Forms![FormName].Visible=False

2. Instead of openning the form later on, all you need to do is set the form
to visible True
3. Create a close button on the form, that will  set the form to visible False

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The problem with this approach is that the data on the form won't be
refreshed, so and data that was entered after the form was loaded wont be
displayed on the form.
To display the data you'll need to refresh the form, and it will be just as
loading it again.
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The approach I'm using is, The combo's don't have any RowSource defined, on
the Got Focus event of each combo I assigned the RowSource for this specific
combo.
In that way the form open quickly, and only the nesecery combo's got
RowSource assigned to them.

Me.[ComboName].RowSource = "Select Field1 From TableName"