Quick answer
The short answer depends on weather, drying, and safety
You should mow your lawn when the grass is dry enough to cut cleanly, the ground is firm enough to avoid rutting, and the next few hours do not bring rain, high wind, or heat stress. That can mean mow now, wait until later today, leave it until tomorrow, or skip this week if conditions stay poor.
The location tool above is the fastest way to check your own forecast, but this page also explains what signals matter so the homepage remains useful before any JavaScript result loads.