With the increasing demand for digital services, requirements for their underlying technologies continue to steadily increase. When originally introduced, virtualization significantly changed the landscape of server provisioning and continues to be the technology of choice for cloud infrastructure. Flexibility has become essential, especially with the explosion of the number of connected devices. One key performance indicator of cloud platforms in regards to flexibility is the time it takes a virtualized instance to be up and running on the hardware. While there are studies measuring that time, none of them include the availability of the service inside the instance. Therefore, we extend the definition of a reachable instance to include the startup time of the actual service, which is closer to real-world examples. In this work we compare for the first time traditional virtual machines (VMs), container virtualization and unikernels in this new key performance indicator to further understand each technology's applicability in actual scenarios. We show that the type of virtualization has an impact on the overhead of service startup time compared to the boot time of the instance. Unikernels achieve the lowest values in both boot time and startup time. The best result we observed for a webserver response to a HTTP request is 40 ms, which is achieved by using MirageOS, and is about a tenth of the time a Docker container needs for the same task.