Delay has nothing to do with which weapon you put in the mainhand. Dual wielding adds the delay of both weapons together and then accounts for delay reduction and haste. Blau/sirocco would have the same number of attack rounds as sirocco/blau. The difference is in weaponskills because the main hand gets most of the action, so you want the higher damage weapon in the mainhand.
In other words since Athame is base damage 31 and blau is base damage 33 you will put blau in the mainhand and athame in the offhand. The "occasionally attacks multiple times" doesn't activate during weaponskills, so the higher base damage goes in the main.
There is only one exception to this rule. Fane Baselard is always mainhanded even if if has less base damage than blau, but that's only because when you offhand it it's crap and starts at base damage 22 instead of 27.
31 dmg 211 delay occasionally attacks twice when fully upgraded. Depending on the double attack proc rate could be an excellent offhand dagger for meriting.
I agree sounds like a main hand delay... curious about the proc rate as well. Although the lower damage occasionally attacks x2, are prolly gonna have the better proc rates. Trying to stir up some data if anyone knows....