VP, we do the same, day and night, VMC or IMC - our required response is 15 mins 0800 - 2200 and 45 mins 2200 to 0800. If the engineers have serviced the aircraft after one job I'm not about to waste time checking oil levels before launching on the next one.
However if it is neccessary to exceed response time in order to do the job safely then we will take any flak that comes and make that decision.
But it is also possible for us to get airborne in under 5 mins from the call if we have to.