that message sounds just right. Send it now and then if you hear nothing further open a dispute on Monday. The buyer then has a further 8 days to pay before you can close the case. (and get your listing fees back)
I usually give a full week before first reminder. When I started selling I was a bit shocked at how slow some payers are as I always pay immediatley on winning but lots of people don't and take a few days. All have paid eventually though - even one poor lady who I emailed three times who had gone in to labour very early. I give at least two reminders - the first is like yours, the second will be a resent invoice with wording along the lines of 'Just a gentle reminder that you have comitted to but this item. Do you still want to buy it ? If I have not heard from you within x days I will notify ebay of an unpaid item so that I can get my listing fees etc back'. I never threaten with a strike but point out they are costing me money
I've been selling quite a lot since January and the items I sell seem to attract buyers new to ebay so unfortunately I've had quite a few non payers so that's why I do one polite reminder and then the dispute after 7 days. I find the ebay message often prompts them into action. I would never threaten strikes or anything like that as it's just not constructive.