To address the anticipated sporadic terabyte demands generated by high-end time-constrained applications, dynamically reconfigurable optical networks services are envisioned. However, the time and rate granularities of a bandwidth reservation service and those of transfer tasks using the reserved capacity is not necessarly in the same order of magnitude. This may lead to poor resource utilisation and overprovisionning. Transfer request aggregation is able to limit this problem. This paper explores the interactions between a bandwidth reservation service and a data mover service guaranteeing bulk data transfers. We formulate the underlying optimisation problem and propose an optimal strategy for bandwidth provisionning when time-constrained bulk data transfer requests are known in advance. Simulations show that the temporal parameters of requests (deadline and patience) are the dominant criteria.