Before revision:  Our model also uncovers power-law relationships for the concentration as a function of time and particle emission rate and for the TTI as a function of ventilation rate and particle emission rate; these may be used as a fast tool to predict the SOT in several realistic scenarios. Finally, we show that wearing a mask of 50\% efficiency could increase the SOT by 98\% and reduce the vacancy time by up to 55\%, depending on the ventilation setting .
After revision:  Our model also uncovers power-law relationships for the concentration as a function of time and particle emission rate and infectiousness of the virus on the TTPI. The model can be easily updated to take into account modified parameter values. This work paves the way for establishing `safe occupancy times' at any location and has direct applicability in mitigating the spread of the COVID-19 pandemic .