I haven't done this in a while but if memory serves correct SMBC always takes a looooong time to soften after it's been in the fridge overnight.  I have to transport a large cake this weekend for a baby shower.  Finished it will be a 6-layer 10" round bottom tier and 8-layer 8" round top tier.  I will fill and decorate the cakes using my usual SMBC recipe the night before.  I always refrigerate the finished cakes (unstacked) overnight (about 8hrs) so they will be nice and firm during transportation (45min drive).  The cake would be served around 1pm on Sunday.  I plan to remove the cakes around 8am that morning and begin transporting around 10am.  I know they will still be very firm even after 2hrs of being out.  I'll reach the venue just before 11am.  There I will stack the cakes, setup display, and make any final touches.  Do you think after 5 total hours of defrosting that my cakes will be soft enough to eat?  Any tips or tricks?  In the end I'd always rather cutting into a cake that's on the cool side versus arriving with a smashed cake in my truck.  If it makes a difference the cake is red velvet.  Thanks in advance!

only observation i have is that -- i don't take my cakes out of the fridge until the minute i put them in the car

I usually travel with my bottom two tiers already stacked, and then pop on the final tier or two (or however many) at the venue. I travel with my cakes as chilled as possible, I don't take them out of the fridge until the rest of the cake kit is in the car and I am ready to go. I usually only use SMBC too and mine is starting to soften up by the time I get to any venue in my city (usually a 30min journey whichever way I go as I'm fairly central), despite the a/c being on full blast. I'd probably aim to arrive around 9-10am with fully chilled cakes, stack and do any final decorations then.

all of my cakes are boxed and they stay cold on the ride in the corrugated cardboard moving boxes -- earlier on i depended on the car's air conditioning -- but what if there's a traffic jam or the car starts to over heat -- y'know 10,000 different things could happen that would not affect the cake's deilvery if if it is kept cold and protected -- but it could melt otherwise