In power systems, the system frequency is a good indicator of the networks resilience to major disturbances. In many deregulated markets, e.g., the Nordic power market, the system operator controls the system frequency manually by calling off bids handed in to a market, called the regulating market. In this paper, we formulate the problem of optimal bid call-off on the regulating market that the system operator is faced with each operating period, as an optimal starting problem with delays. As general optimal starting problems with delays are computationally cumbersome, we present two alternative approximation schemes. First, we make simplifications to the problem that renders classical solution concepts tractable; then, in a second approach, we define a suboptimal solution scheme, based on limiting the feedback information.