You can express the notion 'approximately' with an adverb such as примљрно or приблизќтельно (примљрно двђ часђ 'approximately two hours'), but this is not the conversational way of doing it in either Russian or English.
Both Russian and English allow you to express this notion with a preposition: ћколо + Genitive (ћколо двџх часћв 'about two hours').
Russian has an additional a feature of word order inversion to express 'approximately': put the noun before the numeral (часђ двђ 'about two hours'). To say 'two or three hours' put the two numerals together like this: двђ-трќ часђ. You can also use both of these devices together, see below.
Ї спалђ ћколо двџх часћв. I slept for about two hours.
Ї спалђ часђ двђ.
(Note stress in часђ, which is an irregular form used in telling time.)
(Same translation.)
Ї спалђ часђ двђ-трќ. I slept for about two or three hours.