Time limit

Can a player extend the time if the opp agrees?

The opponent can give more time if the setting is enabled:
lichess.org/account/preferences/chess-clock

Hello,
Hitting the black + sign on blue ground in the upper right corner of the clock adds another 15 seconds to your opponents time. As far as i know has he not to agree.

lichess.org/account/preferences/chess-clock

The option can be disabled in the settings of the clock.