Can I cast the slab and inverted beams separately?

Yes, in cases where casting of slab and inverted beam is not practically possible in one go, you can cast inverted beam after setting of slab or on another day.

After casting of the slab, construction joint need to be made carefully in inverted beam area.
 
Yes, in cases where casting of slab and inverted beam is not practically possible in one go, you can cast inverted beam after setting of slab or on another day.

After casting of the slab, construction joint need to be made carefully in inverted beam area.

Please see that use proper grade bond coat ( bond coat strength to be similar to parent concrete ) preferable to use an epoxy bond coat and ensure that the balance work is completed within 48 hours of casting parent concrete.