To cut across the Okeechobee it will take about 2 to 3 hours. The lake is quite shallow so stay within the markers. There are a couple of places where the markers are to far apart to see. A gps helps here.
You did not mention your draft. If you have GPS and a chart plotter it is a real help. There is nothing to really get in a panic about though, just use good judgment.
Watch the weather, the lake being big and shallow really can kick up in a blow.
I have never taken the rim route around the lake so I cannot help you there. There is a lock right as you come off the lake and I if I remember there is one or two after that. This can really slow you down. give yourself at least a day and a half.
Cap'n Dave. Reporting Live from Staniel Cay