I'd been going to say much the same as bj_cardiff. Depending on breed, if it's safe and works for you to put the tup in with the ewes and lambs now (or soon), do that, so he gets to know everyone and they him, then when you wean the ram lambs you just keep him with them.
The ingredients to when must the ram lambs come out are a) a bit of an age/fitness thing, b) time of year and what the weather is doing and c) breed, mostly of the ewes rather than the tup.
Ex-BH, with a commercial flock up on Hadrian's Wall, used to leave one group of ewes and lambs with a tup through the summer, just to see when the first lambs arrived. Mostly that would be one or two ewes around mid-Feb (so tupped mid-late Sept), with a one-off lamb born one year on 4th Jan (so tupped Aug 10th). Until, that is, we got a Charollais tup and started to bring some of his daughters into the flock. After they reached maturity we had to start taking the tups out much earlier
Until we had the Charollais crosses, some years the ewes would start chasing the tup early Oct; other years, usually when the summery weather continued longer, is might be the second half of October when the majority got active.
Any of the Dorset breeds will come to the tup at any time.
Some people tell you the ewes won't cycle when they are still lactating. Some won't - but some will, though