There are some predefined functions in Exposed (se...

# exposed

[tapac]

There are some predefined functions in Exposed (see in this file https://github.com/JetBrains/Exposed/blob/master/src/main/kotlin/org/jetbrains/exposed/sql/Function.kt) as far as CurrentDateTime.
So in your case you may try:

Tasks.select { 
   Tasks.postTime lessEq CurrentDateTime() and 
   (Tasks.postTime + Tasks.someTime).greaterEq(CurrentDateTime()) 
}