Hi @Anonymous,
Could you please share a screenshot of your flow's configuration?
Could you please show more details about the Forms that you mentioned? Is it the Microsoft Forms?
If the Forms that you mentioned is the Microsoft Forms, I think your thought is correct, we could only select a date from Microsoft Forms. If you want to select a time from Microsoft Forms, I afraid that there is no way to achieve your needs currently.
You could consider take a try to manually type a time and concatenate it with the date that you select from your Microsoft Forms. I assume that you want to create a an Outlook event at 04/28/2018 6:00 AM, I have made a test on my side and please take a try with the following workaround:
Within Inputs field of Compose action, type the following formula:
concat(body('Get_response_details')?['rc787195479ff44329dd91fb703b380a8'],'T06:00:00Z')
Note: The body('Get_response_details')?['rc787195479ff44329dd91fb703b380a8'] expression represents the answer to the Date question in my Microsoft Forms. You could consider select the concat() expression within the expression formula box firstly, then select the Dynamic content tab and simply click the answer of Date question dynamic content of the "Get response details" action. The '06:00:00' represents time part, you could custom it on your side, for example, you want to create an event at 4:35 PM, the time part would be 16:35:00.
Within Start time field of the "Create event (V2)" action, type the output of the "Compose" action.
The flow works successfully as below:

More details about using expression in flow actions, please check the following article:
Use expression in flow actions
Best regards,
Kris