Joshua's long day must have been in the month of Adar.

Adar ended:
February 23 Adar 1, March 23 Adar 1279 BC
March 13 1278 BC
March 1 1277 BC
February 19 Adar 1, March 20 Adar 1276 BC
March 9 1275 BC
February 27 1274 BC
February 16 Adar 1, March 17 Adar 1273 BC
March 6 1272 BC
February 23 Adar 1, March 24 Adar 1271 BC
March 13 1270 BC
March 3 1269 BC
February 20 Adar 1, March 21 Adar 1268 BC
March 11 1267 BC
March 1 1266 BC
February 19 Adar 1, March 19 Adar 1265 BC
March 7 1264 BC
February 24 1263 BC
February 14 Adar 1, March 13 Adar 1262 BC
March 3 1261 BC
February 22 Adar 1, March 23 Adar 1260 BC
March 13 1259 BC
March 2 1258 BC
February 19 Adar 1, March 20 Adar 1257 BC
March 10 1256 BC
February 28 1255 BC
February 17 Adar 1, March 18 Adar 1254 BC
March 6 1253 BC
February 24 Adar 1, March 24 Adar 1252 BC
March 14 1251 BC
March 4 1250 BC
February 21 Adar 1, March 22 Adar 1249 BC
March 11 1248 BC
February 28 1247 BC
February 17 Adar 1, March 19 1246 BC
March 6 1245 BC
February 25 1244 BC
February 14 Adar 1, March 15 Adar 1243 BC
March 5 1242 BC
February 22 Adar 1, March 23 Adar 1241 BC
March 12 1240 BC
March 2 1239 BC
February 19 Adar 1, March 21 Adar 1238 BC
March 9 1237 BC
February 26 1236 BC
February 16 Adar 1, March 16 Adar 1235 BC
March 5 1234 BC
February 25 1233 BC

Therefore January 20 - February 19 marked Adar 1 and February 19 - March 21 Adar 1238 BC, probably the year of Joshua's long day. "If in Adar the sun stands still at noon" may mean Adar 1 or Adar. Then Joshua's long day on the sixth day of the month of the Chinese spring may mean January 26/27 or February 25/26 1238 BC. If the sun moved back five years later to the day, February 25, it would mark the end of the month Adar.