Green’s Dictionary of Slang

nervous, reluctant.

1825		H. Wilson Memoirs II 46: [D]o you know, sir, the thieves have stolen a new water-butt out of our airy, not a week since, and my missis is more timbersome than ever!
1871		H. Holt Golden Bait III 229: Oh , you’re a slippy chap, a shallywalley feller , an’ as timbersome o’ doing yoursel a service as a mealy-mouthed lass o’ saying ‘yes’.