send email (notification) when [Entered date / time] equals to [today's' date /time]

Notifications run off of edits made to the record.  This makes it very difficult to run a notification off of a formula field.  

That being said there is a workaround to this problem.  Set a form rule to auto fill with the user who entered the date.  Then create a report that shows the records where [Entered Date Time] = [Todays Date/Time] and fill it with information you need.  Finally create a subscription that sends this report to that user every day.  This way whoever entered that date will see the records they need to see.   Hope this helps!

Subscriptions do not fire at soecific times. They run once a day in the morning. So it will not work to expect a subscription to run at a specific time and date.

QuickBase can do a daily morning subscription of records which meet some criteria.

Instead of making user to enter a date and time, is there a way to send a notification 7 days before the projected finish where record has not changed? 

You can make a report with any filters you like. Then set up a subscription to send it out daily.

I'm not understanding though what you mean by where a record has not changed.

Thanks. That works great. I meant sending alert without a record being changed.