Addressing past and present injustices in order to create more just futures is the central premise of most social movements. How activists conceptualise and relate to time affects1how they articulate their vision, the actions they take and how they imagine intergenerational justice. Two social movements for change are emblematic of different relationships with time: the struggle to resolve and repair past injustices against Indigenous peoples and the struggle to avert environmental disaster, which haunt the future of the planet. We report ethnographic research (interviews and participant observation) with young activists in these two social movements in New Zealand: Protect Ihumātao seeks to protect Indigenous land from a housing development, and Generation Zero is lobbying for a zero-carbon future. We argue that analysing activists’ articulations and sensations of time is fundamental to understanding the ways they see themselves in relation to other generations, their ethical imperatives for action and beliefs about how best to achieve social change. Protect Ihumātao participants spoke of time as though past, present and future were intertwined and attributed their responsibility to protect the land to past and future generations. Generation Zero participants spoke of time as a linear trajectory to a climate-altered future, often laying blame for the current crises on previous generations and attributing the responsibility for averting the crisis to younger generations. How activists conceptualise time and generational relations therefore has consequences for the attribution of responsibility for creating social change. Understanding and learning about temporal diversity across social movements is instructive for expanding our thinking about intergenerational responsibility which might inform ways of living more respectfully with the planet.