Many ways you could do this.
If you are opening the form from another form you could prompt for the date (Input Box), assign that date to the form's OpenArgs property and as long as the box is checked, each new record could get the date from the OpenArgs property.
You could open the form, enter the date in an unbound textbox then check the box. This could then set the bound control to that date for each new record. If you alter the date, the next record would get the new date if the box is checked.
You could check the box, prompt for a date, set a variable to that date at the form module level and set the bound control to that date for each new record.
You could get the value of the date from the 1st record in the form BeforeUpdate event and pass it to a form module level variable. Then get the variable value and assign it to the date control for the next new record.
Probably 50 other ways to do this. Trick is to choose the right event and perform the correct test(s) and that all depends on the form design and your preferences. I'd say that the Current event must be involved because that's where you must check if it is a new record first, otherwise you could alter the date as you move from record to record.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.