While it's a little counter intuitive it's possible to use the C2 runtime within Construct 3.
Here's a small snippet of the blog post where we announced the C3 runtime
Rebuilding the Construct 3 editor was a huge project. To ensure it was manageable, we kept the same runtime (game engine) that Construct 2 uses, and transferred it across to Construct 3. This is one of the reasons we were able to successfully launch Construct 3 last year, first in beta, and then the full release in December. However we've always planned to replace the runtime later down the line.
That post was over a year ago, since then we've finished the new runtime and set it as the default for new projects ( it's possible to change runtime in the advanced project settings ). However, for projects using the old runtime it's up to the developer if they wish to switch over. One of the common reasons why people are still using the old runtime is that 3rd party addons required rewriting to work with the new runtime, hence some of them are still only available in the C2 runtime. Most of the popular addons have been ported by the original maintainer, or in some cases picked up by a community member with permission and ported. There's a fairly active discussion on the addon forum about porting plugins and looking for versions that support the new runtime.
If you need time since last run could you not just use the unixtime expression?
The current time represented in milliseconds since Jan 1, 1970. This is the standard way time is represented on many systems, and is commonly known as the UNIX time since it originated on UNIX systems.