The constellation Leo is best viewed in the Northern Hemisphere during the late winter and early spring months, specifically from late March to early June.

Here's why:

* Leo is a spring constellation: It rises in the east in the early evening during this period.

* Visibility: As a constellation of the Northern Hemisphere, it is visible at night from locations in the northern hemisphere.

* Optimal Viewing: Leo reaches its highest point in the sky around midnight in late April and early May, making it most prominent and easily observable then.

Keep in mind that the exact timing can vary slightly depending on your specific location and the year. You can use a stargazing app or online resources to find the best viewing times for your location.