My horses are usually trimmed at 5-6 weeks in summer and up to 8 weeks in winter. If I feel they need attention sooner I call my trimmer and sometimes I send her pics. ;) I have a couple who tend to flare(pigeontoed) or run forward(flat feet) and if let go too long you just don't get ahead at all.
I advise telling your trimmer/farrier to not trim any sole off. Allow it to harden up and grow some support while she gets her health back. Boots are a great way to help them over the "rough" spots.
Def want to leave the sole. He usually dosent take too much off anyway. I am going to buy sole guard by vettec. I think it comes off after a few weeks but it sounds like it will help with transitioning.
I like their other product equi pack. I've never seen my mare sound for years with just regular shoes on! One of the hooves lost the pack sometime early this week though. It has been about 4-5 weeks since it was put in, and we didnt take the time to air dry the hoof (my mare is a bugger about standing for the farrier.) I'll give a product review after I try the products out a few times. The equi pack is expensive about $26 and it does 3 hooves for my mare (shes a 0 to a 00 shoe size.) You have to buy the gun and mixing tips or know someone who has them. The stuff dries so fast that you end up using at least 2-3 tips per farrier visit. They arent too expensive though.
I trim my own so usually they get filing at around the 3-4 week mark, and a full trim between 6-8 weeks; it all depends on the horse.
My mare starts mild flaring around 3 weeks, so she gets a good filing, to get rid of the flares, and fix any edges that may be 'scraggly'. She has all white feet, and when I got her she had terribly long, and chipped cracked feet; she's improved greatly with proper care.
The two younger horses I look after have really solid feet, and no flares, so they usually do fine with a strictly 6 week schedule.