Post this question on the very active Arizona forum. They will have the answer for you. I do know that some people plant tomato plants in Arizona in February, since I go there at that time, so I bet you'd be OK starting them now.

Nope, not in your location (assuming you aren't up in the mountains) you still have time to get seedlings in the ground by first week in Sept. and that gives you 90+ days. Use some short DTM varieties. Alternative - if you have plants now use cuttings from them. All explained over on the Growing Tomatoes forum here. Dave

Using a sterile, well moistened seed starting mix, start tomato seeds indoors, 8 - 10 weeks before the last frost date. Sow seeds a quarter inch deep, and cover with plastic to maintain moisture. Seeds will germinate in 10 - 14 days. As soon as seedlings emerge, move to a bright, warm location and keep consistently moist. Select a garden site with well-draining, fertile soil and at least 8 - 10 hours of sunlight each day. Tomatoes can also be grown in large containers filled with potting mix; containers should have adequate drainage. Harden-off the plants one to two weeks before planting outdoors. When temperatures are warm enough, move the plants into the garden. Tomatoes should not be transplanted to the garden until the nighttime temperatures are consistently above 55°F. Set transplants 24 - 36 inches apart in rows 24-36 inches wide. Plant seedlings a little deeper than they were originally grown. Provide support for the tomato plants. Tomato plants need sufficient moisture, about 1 inch of water per week. Crop should be harvested after they are fully developed and ripe. Learn more about growing your own tomatoes by following a few simple steps with this gardening project: Growing Healthy Tomatoes

Well, shoot.. if you already have a fresh squash on hand, then go for it. Do whatever you normally do when you plant your squash seed. It's not really the conditions inside the squash itself that makes the sprouting happen, it's because seeds want to sprout and sometimes inside the squash is a great place to do that. If you got good viable seed, it's going to want to sprout in dirt, damp paper towels, in the squash, smushed open squash in the compost pile.... heck, I've seen squashes randomly sprout where they have been dropped or smashed open in the lawn. As far as I'm aware of, squash seeds don't really require a process to "activate" the seed like some other plants do. They are good to go from the get go.