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As long as they have reached their turning stage (a green stage right before they begin to redden), they will ripen on your windowsill. To tell the truth, covering the bowl will speed up the process and putting a banana in the bowl will speed it up even more. The reason is that tomatoes ripen when exposed to ethylene gas, which they give off naturally. Covering the bowl will trap the gases around the tomatoes, speeding it up. Bananas are major producers of ethylene gas, so putting a banana in with the tomatoes will add even more gas to the process, speeding ripening up even further.

Here is an article that will help you pinpoint the issue.

https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-blossoms-no-tomatoes.htm

If your plants have time to produce depends on your growing zone. If you are in a warmer climate, your plants may have enough time to reach maturity.
On average your plants will need 100 to 125 days from seed to harvest or 75 days from seedling transplant.
Here are some articles with more information.

https://www.gardeningknowhow.com/edible/vegetables/tomato/growing-tomatoes-guide.htm
https://www.gardeningknowhow.com/edible/vegetables/tomato/tips-for-growing-roma-tomatoes.htm

It's more common than you might think but definitely not what you want to see on your growing fruit.

Blossom End Rot is typically a result of plants that are kept in calcium-deficient soil that doesn't drain well. This article may help you identify exactly what the issue is and how to correct it:

https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-blossom-rot.htm

You can start tomato plants any time of the year if you have grow lights to give them an adequate amount of light each day (at least 6-8 hours of bright light). Most people in North America start them indoors in late winter/early spring to be set out after the ground is consistently above 50 degrees Fahrenheit. Tomato plants don't do well in colder conditions.

Your plant is tall and pale; it looks starved for light. Tomatoes typically require 6-8 hours of full sun to grow well and to set fruit. Can you take it outside? Perhaps start with just a couple hours of sun for the first 2 weeks to all the plant to acclimate and then inch up to the full amount.