hi :) felan , aknun and hala : they all mean now, but
1)aknun is the formal form for hala and felan. For example when writing or speaking formal, you are not allowed to say felan ketab mikhanam.You have to say aknun ketab mikhanam.
2)felan and hala both mean now but theres a slight difference between them because felan shows that you are doing a verb right now or you are not doing a verb right now ! but hala just means now, as an adverb of time and these two have the arabic roots.For example when saying hala ketab mikhanam you mean that you are reading a book RIGHT NOW but when saying felan ketab mikhanam you mean I am READING right now and Im not gonna do any thing else other than reading for a while but I have other plans for some time later .
(felna usually has a negative connotation : Im not cooking dinner now, because felan Im reading a book)
Anyway you cannot use any of them for saying here . Here is inja.