You are right, of course BS EN 61008 should trip within 300mS at IΔn. That's what comes of trying to rush stuff.Within 40ms at 5x rated current, so set your meter to 150mA. Depending on RCD, 200 or 300ms at rated current.
A bit academic though, as I rather doubt that the OP's tester (multimeter + a few resistors) has the ability to measure trip times in milliseconds!