AutoTools Tasker question

I am new but the Tasker forum is redirected to a foreign language Google Groups page, so I post it here.

My question is:

I use an expression
if (%TIMES-%Offtime)
...
Endif
%TIMES = builtin variable of current time (e.g. 1560123456)
%Offtime = a variable set by me which contains an earlier time e.g. 1560000000.

which does not work, it appears that arithmetic expressions are not supported.
E.g when I log %TIMES-%Offtime then I see literally "1560123456-1560000000" instead of 123456 which is the numeric result.

Documentation of Tasker lacks anything about how to use arithmetic expressions.

How should I use them ?