Hi Calum, Whatever time you have, Yes it's worth it.
As you say, the challenge now is to decide on your start and finish point, and your likely 'speed'.
It's a rather impossible question to answer I think, which is probably no want you want to hear, but I you might have suspected you would hear
Whatever anyone says is personal opinion of course, and based on their own experiences, fitness and time allowance.
I would merely say this.
I walked from St Jean to Santiago in 40 days. Most people seem to do it in the 33-36 day range. Some are faster, some are slower.
I walked with people who were walking 30+ kms (18 miles) a day. They seemed to have a ball. I couldn't keep up though.
I walked at a more comfortable pace for me. About 22 kms a day was the sweet spot (only 14 miles). I was probably one of the slowest walkers. Luckily I had plenty of time.
So. If you can walk 20 miles a day. Day after day. Comfortably. Then you'll be fine. Depending how fast you actually walk (which should NOT be a speed target) you will arrive by lunchtime or later.
It's also a question of 'hours on the road'. Whilst I was a very slow walker, I still mainly 'kept up' with my Camino family, because I just walked more hours than they did... They would be washed up and on their first drink by the time I crawled into town
Probably the best advice that is shared on this Forum, is not to plan too much! If you plan too much and things go wrong you'll be disappointed. So always have a Plan B a Plan C etc. What if after a few days you find 20 miles a day is too much? Or too little! Stay flexible....
I was just happy to reach the end of each day still able to walk. It was only when I was a few days from Santiago I actually started thinking about the 'end'....
Sorry, rambling on a bit. But you get the idea....