I always try to post next day.
I am happy to combine postage for multiple purchases, i do ask buyers if they are able to pay the full total to pay, and then i will refund the difference from postage cost after have taken items to post office, i just find it easier to do it this way, or you may be able to request an invoice for me to adjust postage cost.
Please take a look at my other items for sale, more items are being listed on a regular basis.