Does conspiracy charges increase time ? Does relevant conduct require conspiracy charges?

It is hard to answer without knowing the specifics. At a minimum, dropping the conspiracy will reduce the maximum penalty. But relevant conduct will still apply even without a conspiracy. It could be, therefore, that the guidelines will not be affected by dropping the conspiracy,

Not enough information to say. If there is more than one person implicated in the conspiracy, then the conspiracy charges will still stand. Just because one drops out doesn't mean the whole case is done. Even if so, relevant conduct from that person Can still be included.

Let's clarify something. Conspiracy in itself is not a crime unless it has some substantive offense. Example would be conspiracy to commit wire fraud. Now, relevant conduct is what each defendant did in that crime. When charged with a substantive crime, wire fraud then only that defendant conduct and amount of loss is used for the sentencing guidelines. If charged with conspiracy wire fraud all the relevant conduct from the time joining the conspiracy of all conspirators is used for calculation. Example 1 guy skims 1 card for 500 dollars that is the loss and number of victims (1). In conspiracy if the guy did only 1 card for 500 but his conspirators did $100k and 2000 victims he would be sentenced for all these amounts and victims. Similar for drugs, weapons, fraud, etc. That is why it is very important to separate from conspiracies in possible pleas and correctly identify join date and limit loss amounts. In conspiracies you may benefit for 1-3 levels of participation minimal participant but these reductions are rarely given. An experienced lawyer might be able to fend situations when the government want to dump everything on a defendant. Best of luck!