Honestly, the extension of the Cave Exploration Rebate duration is a great move in my opinion.
It does benefit a lot of people who either fell short a couple hundred keys from benefiting from the rebate this week and otherwise
would have missed out completely on their rebate.

So long as it doesn't reset the rebate progress, seems like a pretty good idea to utilize for all rebates in my opinion.

I did notice the first step was Ninja Recruitment Rebate being extended to match the duration of Time-Limited Treasure last time it was here
and that itself benefited a lot of people I know. They were able to get the last few scrolls they needed in the following week and achieve their rebate in time.

That said...if you were to increase every rebates duration from 1 to 2 weeks, an event cycle would look something like this:
Week 1 : Battle Armor Rebate & Refinement Rebate
Week 2 : Refinement Rebate & Cave Exploration
Week 3 : Cave Exploration & Ninja Recruitment Rebate/Time-Limited Treasure
Week 4 : Ninja Recruitment Rebate/Time-Limited Treasure & Charm Rebate
Week 5 : Charm Rebate & Battle Armor Rebate

Just something to consider.. We'd always have an active rebate and people have more time to get what resources they can
to participate in them, but that's just me trying to look at this from a positive perspective.