Learn French: Avant de commencer, tu gagnes du temps en hiérarchisant ces projets. - Before starting, you save time by prioritizing these projects.

The gérondif (en + present participle) usually describes how an action is performed, but here it acts as a conditional shortcut. Saying tu gagnes du temps en hiérarchisant is a more elegant way of saying 'If you prioritize these projects, you save time' (Si tu hiérarchises ces projets, tu gagnes du temps).

Why does the sentence use gagnes instead of sauves for 'save time'?

In French, you 'win' time (gagner du temps). The verb sauver means 'to save' in the sense of rescuing someone from danger, or saving a computer file. Saying sauver du temps is a common anglicism that sounds unnatural to French ears.

Why is it avant de commencer rather than avant que tu commences?

When the subject of both actions is the same person (here, tu), French prefers the much simpler structure of avant de followed by an infinitive. You would only use avant que followed by the subjunctive if the subjects were different, such as 'Before he starts, you save time'.

Are you supposed to make a liaison between en and hiérarchisant?

No, you must not make a liaison here. The 'h' in the root word hiérarchie (and its related verb) is an 'h aspiré' (aspirated h). This means it acts like a consonant barrier. You pronounce it as en followed by a tiny pause, then hiérarchisant, completely avoiding connecting the 'n' sound.