Experimental measurment of thiosulphuric acid decomposition kinetics

Problem

I am trying to do a kinetics analysis on the following reaction:

$$ce{Na2S2O3 {(aq)} + 2 HCl {(aq)} -> S {(s)} + 2 NaCl {(aq)} + SO2 {(g)} + H2O {(l)}}$$

Suggested Method

However, most practicals online suggest I use an ‘X’ Mark and let the sulphur precipitate cloud the mark (Here’s an Example) . To measure the rate of the reaction, I would begin timing as soon as I mixed the two solutions and end as soon as the ‘X’ was completely obscured.

Alternatives

However this form of time measurement is somewhat qualitative.

I considered looking at:

• pH or temperature:       Those readings would not provide substantial data.
• Change in volume or mass:   For the gas released, but $ce{SO2_{(g)}}$ is dissolvable in water.
• Conductance:         Although this is viable, I was told there is an alternative.
• Colour (Spectrometry):    This probably won’t work because the spectra observed and                  measured will suddenly reach its maximum as solids are                becoming present that have complete absorption.

I was told that the last option (colour or spectrometry) was “on the right direction”.

Question

So, with all this in mind…

Are there any quantitative means of measuring the rate of the above reaction?