获取数据不能超过30天的数据，这是什么原因

sart_time = '20250201'
end_time = '20250316'
df_full = xtdata.get_local_data(stock_list=['000593.SZ'], period='1d', start_time=start_time, end_time=end_time)

print(df_full)

{'000593.SZ': time open high low close volume amount settelementPrice openInterest preClose suspendFlag 20250205 1738684800000 5.44 5.49 5.41 5.47 41052 22396428.0 0.0 15 5.43 0 20250206 1738771200000 5.46 5.49 5.35 5.49 46936 25509228.0 0.0 15 5.47 0 20250207 1738857600000 5.49 5.56 5.44 5.51 57990 31981402.0 0.0 15 5.49 0 20250210 1739116800000 5.53 5.61 5.52 5.60 53404 29768937.0 0.0 15 5.51 0 20250211 1739203200000 5.61 5.63 5.53 5.57 39108 21778600.0 0.0 15 5.60 0 20250212 1739289600000 5.60 5.60 5.54 5.60 36973 20599906.0 0.0 15 5.57 0 20250213 1739376000000 5.61 5.62 5.52 5.52 38745 21517553.0 0.0 15 5.60 0 20250214 1739462400000 5.51 5.55 5.44 5.46 34072 18697823.0 0.0 15 5.52 0 20250217 1739721600000 5.46 5.58 5.43 5.56 54785 30205868.0 0.0 15 5.46 0 20250218 1739808000000 5.56 5.61 5.38 5.40 53550 29368005.0 0.0 15 5.56 0 20250219 1739894400000 5.42 5.47 5.38 5.45 40856 22199949.0 0.0 15 5.40 0 20250220 1739980800000 5.46 5.52 5.43 5.51 43322 23756515.0 0.0 15 5.45 0 20250221 1740067200000 5.49 5.53 5.39 5.42 56165 30448301.0 0.0 15 5.51 0 20250224 1740326400000 5.44 5.54 5.41 5.48 58229 31960719.0 0.0 15 5.42 0 20250225 1740412800000 5.46 5.48 5.41 5.42 41318 22480745.0 0.0 15 5.48 0 20250226 1740499200000 5.45 5.53 5.43 5.50 44367 24394064.0 0.0 15 5.42 0 20250227 1740585600000 5.51 5.55 5.41 5.53 56068 30702121.0 0.0 15 5.50 0 20250228 1740672000000 5.50 5.60 5.42 5.42 77720 42852899.0 0.0 15 5.53 0 20250303 1740931200000 5.43 5.57 5.43 5.48 65942 36364982.0 0.0 15 5.42 0 20250304 1741017600000 5.44 5.52 5.42 5.51 39148 21480965.0 0.0 15 5.48 0 20250305 1741104000000 5.51 5.53 5.36 5.45 60947 32989951.0 0.0 15 5.51 0 20250306 1741190400000 5.44 5.54 5.41 5.50 58869 32296277.0 0.0 15 5.45 0 20250307 1741276800000 5.49 5.53 5.42 5.45 44544 24400571.0 0.0 15 5.50 0 20250310 1741536000000 5.45 5.55 5.44 5.50 44441 24492609.0 0.0 15 5.45 0 20250311 1741622400000 5.48 5.57 5.45 5.57 68957 38071740.0 0.0 15 5.50 0 20250312 1741708800000 5.60 5.63 5.56 5.58 53083 29621377.0 0.0 15 5.57 0 20250313 1741795200000 5.63 5.63 5.48 5.59 59330 32890301.0 0.0 15 5.58 0 20250314 1741881600000 5.59 5.65 5.54 5.64 71395 40006532.0 0.0 15 5.59 0}