Yes. Just create a column say 'Scheduled' and enter the date/time you want the email to be sent (as seen in this Sample Spreadsheet). Then open the Options dialog and set the 'Scheduled' column in the 'Scheduled Field'. Click the Save button to save changes.
Now click Merge to emails to start the merging process in the background. Note that this process is triggered hourly.
This feature is particularly useful to get over the X emails/day limit google allows you to send.
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