Efficient transfer of patients between facilities is a key component of regionalized critical care systems, but interfacility transfers pose added risks to patients. We created a decision support tool for dispatchers in medical transportation systems which provides estimates of the time to definitive care, the time between receiving the transfer request and patient handoff, which is a key component of dispatch decisions. This tool provides point-estimates of transfer times that are more accurate than the dispatchers own estimates, to support resource allocation and medical triage decisions. However, additional information about the uncertainty of these estimates may further improve dispatcher decision making. This paper describes an observational study conducted with 2 expert and 2 novice dispatchers in a medical transportation service on usage of our prototype decision support tool. In particular, we focused on whether these dispatchers use uncertainty information in their decision process, and how this information should be presented in a tool. We found that uncertainty, as represented by of the spread of possible transfer times (i.e., variability of times), is not currently considered by dispatchers. However, our observations suggest that reliability information (i.e., the trustworthiness of the tool's estimates) would be used. Expert dispatchers would use information about the reliability of estimates to build their trust in the system, while novices should use reliability information to calibrate their trust.