I started seeds indoors in April and here it is Aug 24 and my tomatoes are still not ripe even though the packet claims 60 days to maturity. I'd like to know when the time starts--when the seeds are planted,when they are transferred outdoors, when they blossom or other considerations.

Days to Maturity or DTM is a mystical number. Normally it is based on the location and growing condition of the trial garden where the seeds where taken from. For the rest of the world those seeds will have a wide ranging set of values.

Most seed companies that I know go with DTM from direct sowing or when put in the garden. It should not be from when they blossom.

Where I live, most of the time I can add 1 month+ to most items. Lettuce is one that I am within a week or two, but I have pretty ideal conditions for growing lettuce (cool and foggy - might do with a dash more sun).

Here are some of the things that effect DTM. If you can think of others, please add them:
1. Location (Latitude, longitude and elevation)
2. Weather the year it is grown (sun, rain, temperature ...)
3. Transplanted or sown directly (along with any transplant shock)
4. Soil condition and fertilizer.
5. Some say the phase of the moon.

For vegetables that are not hybrids and that are easy to collect seeds for, you can improve the DTM by finding a variety that does good in your area and replant the seeds so it slowly acclimates to your environment. (I don't think you can make something grown that isn't good for your area, and some plants adapt quicker than others.)