Off topic but I’d divide that 6 by 50% because there’s no rest which gives you 3 hours per workout. Plus there’s plenty of room to increase intensity above what you will be maintaining while remaining submaximal. You can also do two-a-days. Lastly, your training should become more race like as you approach your event so...gasp...go outside. Don’t quote me on that, though

Seriously, though, if you want to train outside, train outside. Indoor training is far superior for load monitoring and management (provided you don’t train indoors like you train outdoors). Is that all there is to cycling? Nope. Is that all there is to performance? Nope.