Compilation of quite simple expression raises the following error:

invalid operation: / (mismatched types time.Time and interface {}) (1:13)
 | (a - b + c) / d
 | ............^

It happens because the binary minus processing has the following check:
https://github.com/antonmedv/expr/blob/2eb6a03aacf9ca8a87685a6f3b1adc3e8473b295/checker/checker.go#L262
And function isTime ends with the following:
https://github.com/antonmedv/expr/blob/2eb6a03aacf9ca8a87685a6f3b1adc3e8473b295/checker/types.go#L101

Changing of return isAny(t) to return false solves this problem.

BTW Compilation of (a + -b + c) / d and (a + c - b) / d expressions are ok w/o above change.