One big source of variability in the length of time and amount of resources it takes to build a venture lies in the type of tehcnology that the venture is built upon.
For example, a company that is deploying a mobile app to consumers can get going in a matter of weeks, if not days. They can then start learning from customers and iterate their offering with new software patches and releases. The barrier to entry is very low and the clock speed is super fast.
On the other hand, a company that is deploying a consumer electronic device, say a wearable health monitor, has to deal with a much slower development process and a longer cycle, simply because it takes time to fabricate tangible things. Sometimes just buying components to put into the device can take weeks. Hardware based businesses therefore have an inherently different cadence to product development. It also takes a lot more up front capital to fund the advanced R&D and prototyping process.
Deep tech or biotech businesses is even more challenging, because they often take on a lot of technical risk up front may have additional fundamental and applied research to do in order to commercialize their technologies. They have a much longer runway than a software startup. For those startups, they may need to rely on grants to make progress before they are ready to raise a round of venture capital funding.