Cryptic answers

[rhu]

Theme: replace abbreviations for units of time with the next-larger unit. Wordplay reflects altered spelling.

Across:
1. ardor (and/or trading R for N)
8. joist (Jo + is + t)
13. boa (Bogota - got)
14. rap (wrap - w)
16. amp (tamp - t)
17. mid (MI + D)
18. Mile High City
19. one ((t)one)
20. HRN [Minn.] (HuRoN)
21. HRK [Mink] (H(R)K)
22. nor (NORAD - ad)
23. agates (Ag + ate + S)
25. etes (fetes - f)
26. YRET [Monet] (hidden)
27. peso (pesto - t)
28. rushed (Ur backwards + shed)
29. neated (nea(rby) + ten (dollar bill))

Down:
2. ROMINUT [rose cut] (Rome - e + in + Ut)
3. duplexes (D + up + le(x)es)
4. Obie ((T)obias + e - as)
5. ROAHRG [roaming] (roa(h)r + g)
6. CAMINARD [case card] (ca(mi)nard; mi is 3rd scale degree)
7. frighten (freight + e + n - e)
8. JASHRE [jasmine] (ja + shre(d))
9. opec (hidden)
10. INMINRET [in secret] (anagram of "trim nine")
11. ski tows (skit + ows)
12. GAMONER [gawker] (Reno + mag, reversed)
15. EDYRTON [Edmonton] (anagram of "d on tyre")
23. ash (as + h)
24. spa (sp + a)

Anything still unclear?