Originally Posted by
Phasers
If you know which route you want to check, why don't you sign up for expert flyer (it is free the first 7 days). Look for C inventory for Y-J SWU upgrade.
But to answer your question, on a particular route, it is easy to check multiple days at once.
I do have an expert flyer subscription but I have had many cases where EF says C=0 and yet the EXP desk says that there is bookable C space so I would rather just get the information straight from the horses mouth.