Roladin, on 24th Ibn Gvirol st., makes fresh doughnuts every day, from about 8:00 and till late night (I bought fresh douhgnuts there at about 22:00). I don't know if they're open on saturdays, but you can call and ask (03-6966177).
Their doughnuts are great (though not cheap), and if they'll tell you they open at 19:00 on saturday, I'd say it's worth the delay.