12 minutes for a stand up change? That seems a very long time to me.
For me (wet only admittedly) I can: prep my new nappy (unfold, brief fold lengthways, stretch the leakguards), de-trouser, un-button onesie, remove old nappy and clean up (wipes and cream if needed), pop new nappy in place and apply powder, before finally fastening (bottom tapes first, adjust and then top taps) and buttoning up me onesie and trousers back on.
Takes about 4 minutes for me, can do it quicker IF in a clean place (ie home!) and being less cautious and where trousers etc touch the floor.