The theme entries are common phrases, rendered pun-ny by the addition of SUR to the beginnings:
17. Scoop a major news magazine? : SURPASS TIME.
27. Sheriff of Nottingham's plan? : SURROUND ROBIN. My favorite entry.
48. Hearst Castle? : SURREAL ESTATE. Situated in the hills above San Simeon.
64. Banner advertising overstocked shelves? : SURPLUS SIGN.
Even though it's a Thursday type of theme with an "add letters" gimmick, the fill seemed incredibly easy, and I finished in nearly typical Monday time. Your experience may vary.
Across
1. Actor who spoke the line, "I'd show him who was king of the forest!" : LAHR. Our cowardly lion from Wizard of Oz.
5. Sharing word : APIECE. DH and I shared a pizza last night, and had three slices APIECE.
11. Newborn nurturer : MOM.
14. Northern terminus of I-79 : ERIE.
15. Frank quality : CANDOR.
16. Andean tuber : OCA.
19. Install, as tiles : LAY. Been there, done that this past year.
20. It often gets blown off : STEAM.
21. Subscriber's gift : TOTE. Handled bag?
22. WWII battleground : ST LÔ. What little was left of the town was bulldozed so troops could advance to the front.
23. Cyberchats, briefly : IMs. Instant Messages.
25. Running wild : ON A TEAR.
32. Bag-screening org. : TSA. Transportation Security Administration.
33. Dent, say : MAR.
34. "The Magnificent Ambersons" director : WELLES. I just watched it last weekend!
37. Pioneering computer : ENIAC.
40. Pony up : PAY.
42. Wool source : LLAMA.
43. Purse counterpart : MAN BAG. Ryan Reynolds sports one well.
45. __ bath : MUD.
47. Gusto : VIM.
52. Anxious place to be : HOT SEAT.
54. Watering hole : BAR. and 36-Down. 54-Across reorder, with "the" : SAME. But not 18-Down. A few rounds, e.g. : AMMO. Another great misdirection.
55. Wind quintet member : OBOE.
56. Ignoring, with "to" : DEAF.
59. Greek restaurant offerings : GYROS.
63. Title for Sean Connery : SIR.
66. President pro __ : TEM. Latin abbr. of "pro TEMpore," for the time being.
67. Release payment : RANSOM.
68. Corrida critter : TORO.
69. Intractable beast : ASS.
70. Sacks out : SLEEPS.
71. Fume : STEW.
Down
1. Not as expensive : LESS.
2. In __: stuck : A RUT.
3. Bring in : HIRE.
4. Get to work again : REPAIR. Great misdirection in the clue!
5. Window units, briefly : ACs.
6. Over : PAST.
7. Fascinated by : IN TO.
8. Text __ : EDITOR.
9. "You can't be serious" : COME NOW.
10. Lyrical "before" : ERE.
11. Eruption output : MOLTEN LAVA. Also MOLTEN LAVA cake.
12. City west of Daytona Beach : OCALA.
13. City boss : MAYOR. RIP, Mayor Menino.
22. Moonshine source : STILL.
24. Dim __ : SUM. C.C. explained to me that Dim SUM and Cha ("tea") are daily fare for retired folks in Hong Kong. The daily social is called Yum Cha ("drink tea.") YUM!
26. Son of Adam : ABEL.
27. Mushroom part : STEM.
28. Annapolis inst. : USNA.
29. Reasons to pull out the tarp : RAINSTORMS. I wanted RAIN "delays" at first. Slowed me down for about 15 seconds.
30. Rest of the afternoon? : NAP.
31. Emmy category : DRAMA. The 2014 winner was "Breaking Bad."
35. Give off : EMIT.
38. Take unfair advantage of, as a privilege : ABUSE.
39. Attention to detail : CARE.
41. Actor Brynner : YUL.
44. Slow and steady : GRADUAL.
46. Cotillion honoree : DEB.
49. Everlasting, to the bard : ETERNE.
50. Yields to gravity : SAGS. I've been yielding for several years now...
51. Hush-hush hookups : TRYSTS.
52. Shade-loving plant : HOSTA. I have about 6 different varieties in my yard. So easy to take care of!
53. Village Voice awards : OBIES. From "Off Broadway."
57. Sanctuary section : APSE.
58. Probably not a really good show : FLOP.
60. Laugh-a-minute type : RIOT.
61. Big brute : OGRE. Poor Shrek. He seems like such a nice guy to me.
62. Put one over on : SNOW.
64. Many AARP members: Abbr. : SRs. Seniors.
65. Hesitant sounds : UMS.