This paper revisits the problem of time synchronization and localization in wireless networks with approximate message passing. A simple yet efficient, approximate Gaussian Belief Propagation (GBP) algorithm for cooperative localization is proposed. Compared to prior art, the algorithm exploits only oneway measurements, as well as simplified equations, not offered before in the literature. The joint time offset and location estimation problem is then studied, and a non-cooperative approximate GBP algorithm is proposed, where agents communicate only with anchors, again with one-way (and not round-trip) measurements. Both proposed algorithms perform close to state-of-the-art methods while offering minimal total communication overhead, which for localization, is smaller by a factor of 100 compared to the prior art.