This expression is used to indicate that the decision or action will be postponed or made at a later time when the circumstances are clearer or more certain. It implies a sense of flexibility and the idea of keeping one's options open. It can be used in a variety of situations, whether it's making plans, responding to a request, or considering a proposal.
For example, if someone asks you if you can meet them for lunch next week, you might respond with "到时候再说" to indicate that you'll decide or confirm closer to the date, depending on your schedule or other factors that may come into play. This phrase is a polite way of expressing uncertainty or the need for more information before committing to a specific course of action.
Overall, "到时候再说" conveys the idea of deferring a decision or action until a later, more appropriate time, allowing for more consideration or evaluation of the circumstances at hand.