Welcome Since!
We in the great gorgeous Pacific Northwest can say plenty about "miserable weather"...it's true that we don't get much snow and our winters are fairly mild in temperature, it is our rainy season, so we get used to about 11 shades of gray on many days!
The info and recommendations from missliz are on the money...and it's totally true that the best training is to get out and ride...if you're training for a long duration (59 days right?) and high daily mileage then, get on your bike and start pedaling!...the 2.5 hr mark is true also, but I find it much easier to be when you're outside and the scenery changes, rather than in spinning, on rollers or a trainer; just my preference as I get bored easily I guess!
Are there bike clubs near you that you can tag along with? When I first started riding, I used to go to the low mileage, social level rides, then gradually worked to longer rides at a faster pace as I grew more experienced and stronger. It's also a great way to learn the good local bike routes in your area. Nothing replaces time in the saddle...and working up to being in the saddle for most of the day, then day after day...it all takes time, so plan it out, don't rush it and keep your goals in mind. If you focus on correct bike mechanics, smooth steady cadence on the pedals, and methodical buildup of miles and time in the saddle, you'll feel yourself get stronger before you know it. Not sure if you can get help from a local mechanic or someone knowledgeable in bike fit, but that's super important...if your butt hurts, it'll be discouraging and you don't want that...A friend of mine is a LBS owner and she tells women right away to pay attention to their saddle and positioning so that they don't "bruise the oh so important girly parts"...her shop mechanics always blush and grin when she starts talking about those sensitive topics, but all us girls appreciate it and learn fast how important it is to our enjoyment of this amazing sport.
Keep making it fun and brisk walking, other sports are fine for cross training, but you'll want to put a good training plan in place to follow, so you can enjoy your 'goal' ride experience successfully and safely. Good luck!