Problem with some functions in lambda expression

Hi,

I am using docker image `kapacitor:1.5.3`
I was trying to use some functions inside lambda expression and got results different than expected eg:
- `int(30s)` - in your documentation it states that:

> Converts a string or float64 into an int64 via Golang’s strconv.ParseInt or simple int64() coercion. Strings are assumed to be decimal numbers. **Durations are converted into an int64 with nanoseconds units**. A Boolean is converted to an int64 where false -> 0 and true -> 1.

but I'm getting error `Cannot call function \"int\" with args (30s: duration), available signatures are [(int), (float), (boolean), (string)].`
- `now() - 30s` - results in error `invalid math operator - for type time`, should this operation be valid?

Is there any other way than using `unixNano(now()) - unixNano("time")` to do basic math operations on time types?