Recent results show that slotless, purely-interval based neighbor discovery protocols, in which time is assumed to be continuous, achieve significantly lower worst-case discovery latencies than time-sloted protocols. In sloted protocols, the discovery of device A by B and vice-versa occurs within the same slot, and hence the latencies for one-way and two-way discovery are identical. However, in purely interval-based protocols, these latencies are independent from each other, leading to longer mean latencies for two-way discovery. In this paper, we propose a cooperative approach to reduce this two-way discovery latency. In particular, each side broadcasts information on the time-period until its next reception phase takes place. The remote device adjusts its beacon schedule accordingly once a first packet is received. Compared to non-cooperative slot-less protocols, this technique can reduce the two-way discovery latency by up to 43%. We propose a theory to model such protocols and show that with an optimized schedule, our proposed protocol achieves considerably shorter mean latencies than all known protocols, while still guaranteeing worst-case latencies that are similar to the best known solutions. For example, compared to Searchlight-Striped, our proposed protocol achieves by up to 89 % lower mean latencies and by up to 86 % lower worst-case latencies.