In that case I would use a ratio. Some googling reveals that the formula for standard error is S.E. = σ/√n , where σ is the standard deviation and n is the number of measurements. Taking n = (rate of measurements)*(time) and assuming the rate of measurements is constant, you can set S.E.(1)/S.E(2)=10=(σ1√T2)/(σ2√T1).