Delivered all 4 in less than 48 hours. Great job!
I just have a question: can I use this service again with the same account if I already have 4 free rides on it? Maybe I should I use the 4 free rides first?

No mate you can use the service again. Don't keep the rides stacked up for months though. Use them as you get them. There's no harm even if you did keep them. But it's always better to use them soon mate.