Power systems with renewable energy penetration increasingly rely on flexible loads to provide ancillary services, including emergency DR renewable energy consumption, peak shaving, and valley filling. However, the demand response (DR) characteristics of diversified loads such as long DR delay time and ramp-up time do not match the high-resolution bidding and fast-response requirements of ancillary services. To address this challenge, this paper proposes a multi-market DR bidding strategy for load aggregators (LAs). First, the specific bidding resolution and response frequency rules of emergency DR, renewable energy consumption, peak shaving, and valley filling are analyzed, leading to the establishment of a market-side time granularity model. Meanwhile, the DR characteristics of flexible loads, including DR delay time, ramp-up time, and duration, are reformulated into a load-side time granularity model based on DR deviation penalty rules. A bilateral time granularity matching framework is then constructed to enable coarse-grained loads to participate in fine-grained markets through coordinated aggregation. To enable the distributed optimization of DR bidding plans and load response schedules under the management of LAs, a multi-market DR bidding strategy based on bilateral time granularity matching framework is developed. Case studies demonstrate that the proposed strategy effectively unlocks the time flexibility of diversified loads, allowing them to participate in multiple markets and maximize economic benefits.