I wasn't fast, but I had at least one downhill where I hit somewhere in the neighborhood of 30mph...as well as some uphills at 7mph--but that is still faster than I can run uphill, so there's that. I had several steady-state miles in the 16-18mph range, so maybe I can complete that 30k (18.6 miles) in roughly an hour if I have a good day and the first 5k run doesn't burn me out too badly. I may not have much less for that last 5k run, but I will definitely feel happy if I can complete the ride portion without a dropped chain or flat tire. A tire issue would potentially spell DNF.
Right now that is my biggest worry on these solo rides, too. The people in online tutorials make changing a tube look straightforward and fast. But they forget to mention that those friggin' tires are HARD to get off and on. At least I found this to be the case when the hubby was walking me through a practice tire change today. It's definitely the sort of thing that would be easier with an extra set of hands to support the bike for getting the wheel off the bike and then back on, again, too.
Last night we had a really fun time with the rest of DH's JDRF ride team at the ride season kick-off party (ie too much food, so the extra miles I ended up riding today were really necessary). This year he is the assistant/co-coach. So having my no-nothing butt around is good coaching practice for him, as he will likely be showing others how to do things like change flats and basic bike tweaking and maintenance.