What is "regional", but relating to time instead of location?

Solution 1:

contemporaneous -

existing or happening during the same time period

Vis-à-vis the word contemporary, the very similar word contemporaneous can be used when you want an adjective for things events which were contemporary to each other, but in the past. Shakespeare's career as a playwright was contemporaneous with the settlement of Jamestown. They were contemporaneous, they are not contemporary.

Solution 2:

Consider contemporary in its following senses (source):

• existing, occurring, or living at the same time; belonging to the same time: Newton's discovery of the calculus was contemporary with that of Leibniz.

• of about the same age or date: a Georgian table with a contemporary wig stand.

Solution 3:

I'm surprised no one has mentioned temporal.

AHD gives:

1. Of, relating to, or limited by time: a temporal dimension; temporal and spatial boundaries

W3NID gives:

3. a. of or relating to time as distinguished from space

And Oxford Dictionaries Online gives:

2. Relating to time:
 the spatial and temporal dimensions of human interference in complex ecosystems
 This issue explores some of the temporal and political dimensions of art.

In fact, you can find it paired with regional occasionally, as in the respective titles of the 2007 paper Causes of Regional and Temporal Variation in Paleoindian Diet in Western North America and the 2015 paper Temporal and Regional Regulation of Leptin Sensitivity by Diet and Circadian Time.