Currently working on losing fat and doing AM SS .

Started at 30 mins , now doing 50 mins on spinning bike , also do weights 3-4 times a week

I want to kick up the cardio a little and thinking of AM SS and PM HIIT on off days plus swapping out one of the weight days for this as well .

Guess questions as follows

Good idea ?
PM HIIT would be fueled , should it be followed by same post workout shake I would have after weights (40 g whey and Dextrose 20-30g ) ?

I am making good progress on the SS but 50 mins is about the max I will sustain on that out of boredom ( SS is sometimes unfueled except for coffee but sometime is also after some protein or food , just depends how I feel on the day)

Is there an agreed fixed period of SS that is regarded as optimal ?
Would that be different if you had eaten - ie unfueled do max of 40 mins , fuelled xyz mins or as much as you like before you brain explodes from boredom .