“Fast” describes the vessel, not the whole trip. Count the journey to the terminal, check-in time, crossing, and the way back.
Two different operating models
Gozo Channel carries cars and passengers from Ċirkewwa and operates a 24-hour service subject to conditions. Gozo High Speed carries passengers from Valletta or on its Sliema–Buġibba–Gozo service. Those departures are scheduled, with some later sailings subject to seasonal or day-of-week notes.
A traveller in Sliema who can walk to The Strand may prefer the direct coastal route via Buġibba. A driver in northern Malta may find Ċirkewwa simpler. If you plan to stay in Gozo late, look at the return departure before choosing the outward one.
Open the ferry desk to compare route boards, then verify the exact day on the operator timetable. A weather forecast alone cannot tell you whether a boat will sail.