Recently introduced processors such as Tilera's Tile Gx100 and Intel's 48-core SCC have delivered on the promise of high performance per watt in manycore processors, making these architectures ostensibly as attractive for low-power embedded processors as for cloud services. However, these architectures space-multiplex the microarchitectural resources between many threads to increase utilization, which leads to potentially large and varying levels of interference. This decorrelates CPU-time from actual application progress and decreases the ability of traditional software to accurately track and finely control application progress, hindering the adoption of manycore processors in embedded computing. In this paper we propose Progress Time as the counterpart of CPU-time in space-multiplexed systems and show how it can be used to track application progress. We also introduce TimeCube, a manycore embedded processor that uses dynamic execution isolation and shadow performance modeling to provide an accurate online measurement of each application's Progress Time. Our evaluation shows that a 32-core TimeCube processor can track application progress with less than 1% error even in the presence of a 6× average worst-case slowdown. TimeCube also uses Progress Times to perform online architectural resource management that leads to a 36% improvement in throughput compared to existing microarchitectural resource allocation schemes. Overall, the results argue for adding the requisite microarchitectural structures to support Progress Time in manycore chips for embedded systems.