The gas$-$phase reaction A $->2$R $+3$S was carried out in a sealed reactor at constant volume, operated isothermally at $430$ K and $500$ K$.$ In both cases, pure reactant A was fed at $2\mathrm{.}6$ atmospheres of pressure. The experimental results are shown in the following table:

Determine how long it takes to reach an $85\%$ conversion at $500$K$.$