Check for overlapping datetime

[chrishajer (Chris (Gravity Forms))]

I see that you opened a new topic, so we can continue there:

How to write date queries against gravity form longtext gf_entry_meta

I have a form which takes a date time entry. I now need to write a SQL query to check for overlap as a validation but have just discovered that the data type is longtext. Does anyone have any suggestions for how to do a date query in this context? We are dealing with less than 1000 entries.