Based on the usual formula, your 25 time suggests you'll do a 2:01, but realistically your 59 on the H25/1 is probably a better guide, in which case 2:03 or 2:04 seems more realistic. If you get under 2:05 you can consider it a success as a début.
That 59 was a horror show though, I did half of it on the base bars thinking about quitting, because it was too hot and I needed a drink.
I'll go with 2:05 as a guide to try and beat. My disc punctured this morning so me finishing is dependent on the Zefal puncture spray stuff holding up.
@umop3pisdn @mdcc_tester thanks both, that's really useful.
Next question: what time should I be happy with?
PBs are 22:54 for a 10 and 57:55 for a 25, both on decent H courses.
I'd love to get under 2 hours, but what would a good first effort be?