diff --git a/src/lib/time/mutation.cpp b/src/lib/time/mutation.cpp
index 3a8ae6681..6555c22b4 100644
--- a/src/lib/time/mutation.cpp
+++ b/src/lib/time/mutation.cpp
@@ -104,7 +104,7 @@ namespace time {
   
   /** 
    * concrete time value mutation:
-   * impose fixed new start time.
+   * set a new overall duration for an extended timespan.
    */
   class SetNewDuration
     : public ClonableMutation
@@ -143,6 +143,46 @@ namespace time {
     };
   
   
+  /** 
+   * concrete time value mutation:
+   * adjust the given time entity by an offset amount.
+   */
+  class ImposeOffsetMutation
+    : public ClonableMutation
+    {
+      Offset adjustment_;
+      
+      virtual void
+      change (Duration& target) const
+        {
+          imposeChange (target, TimeVar(target)+=adjustment_);
+        }
+      
+      
+      virtual void
+      change (TimeSpan& target) const
+        {
+          imposeChange (target, TimeVar(target)+=adjustment_);
+        }
+      
+      
+      /** @note the re-quantisation happens automatically
+       *  when the (changed) QuTime is materialised */
+      virtual void
+      change (QuTime& target)   const
+        {
+          imposeChange (target, TimeVar(target)+=adjustment_);
+        }
+      
+      
+    public:
+      explicit
+      ImposeOffsetMutation (Offset adj)
+        : adjustment_(adj)
+        { }
+    };
+  
+  
   
   /** Convenience factory to yield a simple Mutation changing the absolute start time.
    *  This whole procedure might look quite inefficient, but actually most of the
@@ -170,6 +210,17 @@ namespace time {
   }
   
   
+  /** Convenience factory: simple Mutation to adjust the duration or length of a timespan
+   * @throw error::Logic when attempting to change the "duration" of a quantised time point
+   * @return EncapsulatedMutation, carrying the new duration value to impose
+   */
+  EncapsulatedMutation
+  Mutation::adjust (Offset change)
+  {
+    return EncapsulatedMutation::build<ImposeOffsetMutation> (change);
+  }
+  
+  
   EncapsulatedMutation
   Mutation::nudge (int adjustment)
   {
diff --git a/src/lib/time/mutation.hpp b/src/lib/time/mutation.hpp
index fd66bb010..13c1b6bca 100644
--- a/src/lib/time/mutation.hpp
+++ b/src/lib/time/mutation.hpp
@@ -105,6 +105,7 @@ namespace time {
       
       static EncapsulatedMutation changeTime (Time);
       static EncapsulatedMutation changeDuration (Duration);
+      static EncapsulatedMutation adjust (Offset);
       static EncapsulatedMutation nudge (int adjustment);
       
     protected:
diff --git a/src/lib/time/timevalue.hpp b/src/lib/time/timevalue.hpp
index d7fe90b30..aa08c00ca 100644
--- a/src/lib/time/timevalue.hpp
+++ b/src/lib/time/timevalue.hpp
@@ -198,6 +198,9 @@ namespace time {
         {
           return TimeValue(std::llabs (t_));
         }
+      
+      // Supporting sign flip
+      Offset operator- ()  const;
     };
   
   //-- support linear offset chaining ---------------
@@ -224,6 +227,11 @@ namespace time {
     return factor*distance;
   }
   
+  inline Offset
+  Offset::operator- ()  const
+  {
+    return -1 * (*this); 
+  }
   
   
   
diff --git a/src/proc/asset/meta.hpp b/src/proc/asset/meta.hpp
index 77e08b71a..9ac73ea4f 100644
--- a/src/proc/asset/meta.hpp
+++ b/src/proc/asset/meta.hpp
@@ -48,7 +48,7 @@
  ** and can be another already existing asset::Meta (inheriting from meta::Descriptor)
  ** Generally this yields a Builder object, which can be used for outfitting the new
  ** or changed metadata entry, finally \em committing this builder to yield a new
- ** asset::Meta (which, in case of a mutation, might superseede an existin one).
+ ** asset::Meta (which, in case of a mutation, might supersede an existing one).
  ** 
  ** @see asset.hpp explanation of assets in general
  ** @see MetaFactory creating concrete asset::Meta instances
@@ -120,7 +120,8 @@ namespace asset {
     public:
       static MetaFactory create;
       
-      virtual const ID<Meta>& getID()  const    ///< @return ID of kind Meta 
+      /** @return ID of kind Meta */
+      virtual const ID<Meta>& getID()  const 
         { 
           return static_cast<const ID<Meta>& > (Asset::getID());
         }
diff --git a/tests/lib/time/time-mutation-test.cpp b/tests/lib/time/time-mutation-test.cpp
index 3a973763b..65bd35612 100644
--- a/tests/lib/time/time-mutation-test.cpp
+++ b/tests/lib/time/time-mutation-test.cpp
@@ -157,9 +157,30 @@ namespace test{
       
       
       void
-      mutate_by_Offset (TimeValue o, Offset change)
+      mutate_by_Offset (TimeValue original, Offset change)
         {
-          TestValues t(o);
+          TestValues t(original);
+          TimeValue& should_be(t.var+=change); // use as ref for verification
+          
+          CHECK (t.span == original);
+          CHECK (t.span != should_be);
+          t.span.accept (Mutation::adjust (change));
+          CHECK (t.span == should_be);
+          
+          t.dur.accept (Mutation::adjust (change));
+          CHECK (t.dur  == should_be);
+          
+          t.quant.accept (Mutation::adjust (change));
+          CHECK (t.quant == should_be);
+          
+          // adjustment is cumulative
+          EncapsulatedMutation back_off = Mutation::adjust (-change);
+          t.span.accept (back_off);
+          CHECK (t.span == original);
+          t.span.accept (back_off);
+          t.span.accept (back_off);
+          t.span.accept (back_off);
+          CHECK (t.span == Time(original) - 3*change);
         }