Yes, if your contract has off-peak hours: Voltaback applies the off-peak tariff to charges made during your slots, and the peak tariff the rest of the time. The slots come from your Linky meter when it is connected to Voltaback. You don't enter them yourself.
Where to see them
Website: "Your Account", "Home" tab, then "View contract details". The "Your electricity contract" window shows the "Tariff Calendar", the "Off-Peak Period" and the prices.
App: the gear icon at the top right ("Account" screen), "My equipment", "My homes", your home, then "View contract details".
A specific charge: its details page shows the "Tariff breakdown" between "Off-peak hours" and "Peak hours".
A charge that overlaps your slots is split: the energy of each portion is counted at the tariff of its slot.
No "Off-Peak Period" line? Your contract has no off-peak tariff, or it shows "Contract in setup".
Correct them
Your option or your prices have changed (switch from Base to off-peak hours, new provider): "Update my contract" with your latest bill (see "I've changed home or electricity contract"). If your Linky meter is connected, the update also re-reads your slots. The new tariff applies from that day, or once the check is complete if the screen shows "Your new contract is being checked": charges already made keep the old one.
Your slots don't match your contract: write to us from the chat with a screenshot of "View contract details" and the document from your provider that shows your slots.
No "Update my contract" button: on the regulated tariff, the screen says "Your prices evolve automatically".