The actual TCAS Resolution Advisory (RA) Thresholds:

below 1000 feet MSL - RA inhibited-N/A
1000 - 2350 feet ------ 15 sec --- 300 ft
2350 - 5000 feet ------ 20 sec --- 300 ft
5000 - 10000 ft ------ 25 sec --- 350 ft
10000-20000 ft ------ 30 sec --- 400 ft
20000-42000 ft ------ 35 sec --- 600 ft
42000-above ---------- 35 sec --- 700 ft