Today, the study of energy efficient networking solutions in sensor networks has been focusing on networks with always-on connectivity between communication end-points and short link delays. However, these assumptions are not true for networks with very long propagation delays such as Underwater Sensor Networks (UWSNs) or networks with intermittent connectivity. In such networks, idle energy expenditure, which includes energy spent on node rendezvous and idle waiting, becomes significant, and renders conventional data transport inefficient. In this work, we leverage characteristics that are unique to such networks, i.e., long-delay tolerability and low duty-cycles, to improve idle energy efficiency. To this end, we propose a staged transport protocol, aDapTN, that adopts a store-and-forward transport paradigm with an asynchronous wakeup scheme. We evaluate the idle energy efficiency of our approach through both analysis and simulation. Our results show that aDapTN achieves much better idle energy efficiency than conventional approaches. The increased latency is a function of parameters for node rendezvous, which can be adjusted depending on the application.