Your paycheck covers BASE. Your day job is your training ground. Use both deliberately.
Your day job is the most generous investor you will ever have. It asks for no equity, demands no repayment, provides health insurance, and lets you keep 100% of what the new business earns.
Your day job is also training you. Every task you perform has a duration — that data becomes your future estimating library. Pay attention to how your employer schedules, communicates, handles change orders. Watch their mistakes too — every one is a free lesson.