Looks great, the new Timeline feature. Though it is obviously not easy for some sites to find an appropriate reference for the assignment.
As I'm not a specialist in geology, I would start with a few rather easy sites:
Danube Delta (Romania) - Holocene
"The modern Danube Delta began forming after 4,000 BC in a gulf of the Black Sea, when the sea rose to its present level. A sandy barrier blocked the Danube gulf where the river initially built its delta. Upon filling the gulf with sediments, the delta advanced outside the barrier-blocked estuary after 3,500 BC building several successive lobes." (Wiki)
Laurisilva Madeira (Portugal) – Eocene or Oligocene or Miocene? I'm not sure about the rules in cases when a site extends over several periods.
"Fossil evidence shows that laurisilva flora once covered much of southern Europe in the Tertiary era, 15-40 million years ago, and what is now seen in Madeira is the largest surviving relict of a virtually extinct flora of great interest." (Advisory Body Evaluation)
Garajonay National Park (Spain) - Eocene or Oligocene or Miocene?
"Some 70% of the national part is woodland with Laurisilvia canaria dominant. The Garajonay National Park has a recorded flora of 450 species of which 34 are endemic to the island and of these, eight species are restricted to the national park. This type of vegetation assemblage resembles that of the Tertiary period which has largely disappeared from southern Europe due to climatic changes." - so, very similar to Laurisilva Madeira (ABE)
Donana National Park (Spain) – Miocene or Pliocene?
"The marshes of the Guadalquivir River constitute an example of geological processes during the Pleistocene. Donana contains the last marshes of the Guadalquivir unaltered by agriculture or development. The marshes result from a subsidence of the continental plate in the Upper Miocene and Lower Pliocene, which caused a depression later filled by fluvial and aeolic deposits. Deposition of a coastal sand bar and mobile dunes continue today." (Advisory Body Evaluation)
Primeval Beech Forests (Slovakia/Ukraine/Germany) - Holocene
"Beech reached Western and Eastern Carpathian territory in an Epiatlantic period 5.000 years ago." (Nomination file, 2007, page 33)
"Consecutively initiated from south to north, old forest habitats have been undergoing a development into extremely differentiated beech forest landscapes for some 6,000 years."
(Nomination file, extension 2011, page 11)