“où”, without doubt.
“pendant laquelle” would have been valid, also.

Technically, both où and quand are usable in such sentences but the resulting meanings are very different.

“une époque où” means “a period of time when” just like “un lieu où” means a “a place where”. This is the correct form here.

Le dix-huitième siècle était une époque où il n’y avait pas de technologie avancée.

“statement A quand statement B” means “when statement B, statement A.”

The second form is meaningless with the question statements, that would be the dubious “When there was no advanced technology, the eighteen century was a time.”

It would be used for example in:

L’information circulait moins vite quand il n’y avait pas de technologie avancée.

(I’m not a French teacher, I’m just French)

Even if où is correct, it sounds more idiomatic and elegant to me to use one of these:

• durant laquelle
• au cours de laquelle
• à laquelle

Le XVIII^ème siècle était une époque durant laquelle il n’y avait pas de technologie avancée.