After beating the normal staff ghosts by a certain margin of time, you can unlock the Expert staff ghosts. The following are the approximated times for unlocking them.
Mushroom Cup
Luigi Circuit
Normal Staff Ghost Time: 01:29.670
Unlock Time: 01:25.742
Moo Moo Meadows
Normal Staff Ghost Time: 01:37.856
Unlock Time: 01.33.571
Mushroom Gorge
Normal Staff Ghost Time: 02:16.110
Unlock Time: 02.07.755
Toad's Factory
Normal Staff Ghost Time: 02:22.480
Unlock Time: 02.15.681
Flower Cup
Mario Circuit
Normal Staff Ghost Time: 01:44.777
Unlock Time: 01.39.183
Coconut Mall
Normal Staff Ghost Time: 02:30.764
Unlock Time: 02.24.788
DK's Snowboard Cross
Normal Staff Ghost Time: 02:34.693
Unlock Time: 02.24.725
Wario's Gold Mine
Normal Staff Ghost Time: 02:19.583
Unlock Time: 02.14.932
Star Cup
Daisy Circuit
Normal Staff Ghost Time: 0:56.822
Unlock Time: 01.48.791
Koopa Cape
Normal Staff Ghost Time: 03:03.022
Unlock Time: 02.54.897
Maple Treeway
Normal Staff Ghost Time: 02:58.633
Unlock Time: 02.50.229
Grumble Volcano
Normal Staff Ghost Time: 02:28.237
Unlock Time: 02.19.524
Special Cup
Dry Dry Ruins
Normal Staff Ghost Time: 02:30.949
Unlock Time: 02.21.681
Moonview Highway
Normal Staff Ghost Time: 02:16.802
Unlock Time: 02.07.016
Bowser's Castle
Normal Staff Ghost Time: 03:04.836
Unlock Time: 02.55.017
Rainbow Road
Normal Staff Ghost Time: 03:05.895
Unlock Time: 02.59.293
Shell Cup
GCN Peach Beach
Normal Staff Ghost Time: 01:34.233
Unlock Time: 01.30.698
DS Yoshi Falls
Normal Staff Ghost Time: 01:16.461
Unlock Time: 01.12.901
SNES Ghost Valley 2
Normal Staff Ghost Time: 01:06.595
Unlock Time: 01.03.752
N64 Mario Raceway
Normal Staff Ghost Time: 02:14.799
Unlock Time: 02.07.915
Banana Cup
N64 Sherbet Land
Normal Staff Ghost Time: 02:48.651
Unlock Time: 02.37.784
GBA Shy Guy Beach
Normal Staff Ghost Time: 01:45.568
Unlock Time: 01.39.255
DS Delfino Square
Normal Staff Ghost Time: 02:41.807
Unlock Time: 02.33.107
GCN Waluigi Stadium
Normal Staff Ghost Time: 02:32.882
Unlock Time: 02.24.645
Leaf Cup
DS Desert Hills
Normal Staff Ghost Time: 02:10.233
Unlock Time: 02.01.141
GBA Bowser Castle 3
Normal Staff Ghost Time: 02:58.304
Unlock Time: 02.50.637
N64 DK's Jungle Parkway
Normal Staff Ghost Time: 02:58.264
Unlock Time: 02.49.028
GCN Mario Circuit
Normal Staff Ghost Time: 01:59.771
Unlock Time: 01.55.267
Lightning Cup
SNES Mario Circuit 3
Normal Staff Ghost Time: 01:38.880
Unlock Time: 01.34.828
DS Peach Gardens
Normal Staff Ghost Time: 02:34.894
Unlock Time: 02.29.006
GCN DK Mountain
Normal Staff Ghost Time: 02:57.744
Unlock Time: 02.50.248
N64 Bowser's Castle
Normal Staff Ghost Time: 03:19.323
Unlock Time: 03.06.723
