Use 'buckle down' when someone needs to focus intensely on a task or study.

Concentration Required

Suggests there is limited time to complete a serious task.

Time Sensitivity

Implies starting a task that has been delayed or procrastinated.

Applies when confronting obstacles or doing something one might be avoiding.

Can denote getting emotionally prepared for hardship or discomfort.

Suggests mental preparation needed before tackling a daunting task.