Note that it says less than one character. A character in UTF-8 can be composed of multiple bytes.

The encoding scheme is laid out in the linked email. Based on the high bits it's possible to detect when a new character starts. Relevant portion:

  We define 7 byte types:
  T0 0xxxxxxx      7 free bits
  Tx 10xxxxxx      6 free bits
  T1 110xxxxx      5 free bits
  T2 1110xxxx      4 free bits
  T3 11110xxx      3 free bits
  T4 111110xx      2 free bits
  T5 111111xx      2 free bits

  Encoding is as follows.
  >From hex Thru hex      Sequence             Bits
  00000000  0000007f      T0                   7
  00000080  000007FF      T1 Tx                11
  00000800  0000FFFF      T2 Tx Tx             16
  00010000  001FFFFF      T3 Tx Tx Tx          21
  00200000  03FFFFFF      T4 Tx Tx Tx Tx              26
  04000000  FFFFFFFF      T5 Tx Tx Tx Tx Tx    32

[...]

  4. All of the sequences synchronize on any byte that is not a Tx byte.

If you are starting mid-run, skip initial Tx bytes. That will always be less than one character.