Time is free, but it's priceless

आयुषः क्षण एकोऽपि
न लभ्यः स्वर्णकोटिभिः ।
स चेन्निरर्थकं नीतः
का नु हानिस्ततोऽधिका ॥

- चाणक्यनीतिः

Alternately,

आयुषः क्षण एकोऽपि
सर्वरत्नैर्न लभ्यते ।
नीयते स वृथा येन
प्रमादः सुमहानहो ॥

Not even a single moment of life can be bought with all the gold and jewels on earth. Therefore, one should utilize every single moment, failing which leads to an irremediable disaster.

Time is free, but it's priceless.
You can't own it, but you can use it.
You can't keep it, but you can spend it.
Once you've lost it, you can never get it back.