The time charter rate is a locked rate for a long time. The timing means the management may think now BDI is good enough for them to negotiate new rate. The $24,000/day means they may still think the spot rate may drop under that bar some day. It reflects their caution to lock the profit asap.
Spot rates are almost always higher than time charters. This ship was chartered at 10.5 to 13.5 months. Therefore, it was leased at a lower rate than the spot rate. Time charters are set at a lower rate because the contract gives a stable business coming in. Also spot rates are for a single voyage in which the owner typically pays for port, canal and fuel costs.
You posted a good explanation of the spot rate vs. time charter. Now that GNK has about 57% of their ships booked for time charter in 2010. I assume the other 43% ships are either moving for a single voyage or waiting for business (less likely they will have their ships wait). When these ships complete their journey, do they get another business with spot rate right away or they have to find business? How does that work? Thanks.