The success of Vietnam in controlling the spread of COVID-19 in the initial stages of the pandemic hinges on their timely implementation of containment and rapid tracing and testing. In this work we examine the temporal aspects of the lockdown in Ho Chi Minh City (HCMC) during the spread of the SARS-Cov-2 Delta variant. A minimal compartmental model with containment is fit to model disease transmission in HCMC. The severity of the lockdown is estimated from Google mobility index and coupled to the infection rate. Various scenarios on when to begin a lockdown and its duration are assessed. This study contributes to Vietnamese health security and policy making by promoting data-driven decision-making. In particular, it suggests preemptive and early lockdowns of at least 3 weeks.