In this paper, we propose the notion of partial time abstraction for timed process algebras, which introduces the possibility to abstract away parts of the timing of system behaviour. Adding this notion leads to so-called partially timed process algebras and partially timed labelled transition systems. We describe these notions, and generalise timed branching bisimilarity to partially timed branching bisimilarity, allowing the comparison of systems with partial timing. Finally, with several examples and a case study, we demonstrate how partial time abstraction can be a useful modelling technique for timed models, which can lead to rigorous minimisations of state spaces.